I read in the  about a puzzle given to 8-year old in Vietnam.      Enter the digits 1 to 9 into the following grid so that the equality holds     Now, given access to a computer, this can be solved easily in a minute or so. My  is 19 lines of codes (8 of which is indentation).  What I'm interested in is whether there is a general algorithm better than the brute force for solving problems such as this one. My code found 136 solutions out of 9! = 362,880 possible arrangements of 1-9. So, is there a strategy better than randomly finding a solution once in ~2403 (362,880/136) attempts. In other words, if you were given this problem in Putnam, how would you approach it.  edit: assume regular order of operations, i.e. the "snake" plays no role


Why $ a^n\bmod\ m = a^{n\bmod (m-1)}\bmod m $ is true when $m$ is a prime number?

I know from Fermat's little theorem that $a^{m-1}\bmod m \equiv 1\pmod m $ when $m$ is prime number. But I don't understand how we got $ a^n\bmod m = a^{n\bmod (m-1)}\bmod m  $ from Fermat's little theorem when $m$ is a prime number.


How do I politely tell a student to take a shower?

There's a student in my class who obviously has some serious body hygeine issues. To preface, this is a fairly packed class -- about 60 students in a small lecture room.  The class is about 2 hours long. The problem has been so bad that when the student comes up to ask a question the stench hits hard. The problem is so bad lately that in the past month, people will leave a seat distance away from this one person, even standing up for the entirety of the lecture just to avoid sitting next to this person when the only seats available are next to the person.   I don't know how to approach him and to ask that they take care of their body. Or will I be a prude if I do try to get him to shower? Maybe it's a unique body issue that he can't fix (unlikely), but I really want to solve this before exams come up, which are going to cause issues. No one has come up to talk to me privately about it but the problem is incredibly obvious.  What should I do?


Prove that V contains a subspace of each dimension

Let $V$ be an $n$-dimensional vector space over $\mathbb R$. Prove that $V$ has a subspace of dimension $r$ for each $0 \le r \le n$.  Is this as simple as saying that $V$ has a basis of $n$ elements, and then take $r$ elements from this basis and this will generate an $r$-dimensional subspace? Or am I missing something? It seems too simple.  Thanks


I have a huge table, and I want the table to fit all the entire page in the horizontal direction. However, the table doesn't fit the page, and the columns were cut. I'm looking for a way to reduce the size and adjust the page. The output for my table is the one from the image as you can see it only show 4 columns, and they are cut. \begin{landscape} \begin{table}[htpb] \centering \begin{adjustbox}{max width=\pagewidth} \begin{tabular}{*{13}{|c}|}


I had a oil burning candle in a dark room and noticed a small shadow on the ceiling directly above the flame.  Its as though the candle throws light outwards in every direction except straight up.  I'm curious as to why it does this. Perhaps its due to the conical shape of the flame?


I initially asked this question on MSE, but then thought it would appropiate to ask it here as well ( correct me if I'm wrong):   A well-known application of the MVT is to prove that any $f: \mathbb{R} \to \mathbb{R}$ with $f'= 0$ is constant. But of course, the MVT relies fundamentally on the properties of $\mathbb{R}$, and in particular does not hold in $\mathbb{Q}$. A standard counter-example is the function $f :\mathbb{Q} \to \mathbb{Q}$ defined by $ f(x)=0 $ if $ x <\sqrt{2}$, and $f(x)=1$ if $ x > \sqrt{2}$, for this function is locally constant. There are several ways of thinking about the difference between $\mathbb{R}$ and $\mathbb{Q}$ : $\mathbb{R}$ is connected while $\mathbb{Q}$ is totally disconnected, closed bounded intervals are compact in $\mathbb{R}$, but not in $\mathbb{Q}$, $\mathbb{R}$ satisfies the least upper bound axiom, $\mathbb{Q}$ does not.   Now, I wanted to see how far one could push this counterexample - is there a function $f :\mathbb{Q} \to \mathbb{Q}$ such that $f'=0$ and $f$ is strictly increasing? Clearly, any slight modification of the usual counterexample where $f$ is locally constant will not do. Also, one can show that if $f$ is uniformly differentiable with derivative zero, it must be constant, even in $\mathbb{Q}$, so I knew I was looking for non-uniformly differentiable but still differentiable $f$.   Eventually, I came up with a construction, albeit not a very explicit one: the idea is that, since $\mathbb{Q}$ is countable, one can enumerate it $q_{1}, q_{2}, q_{3}, \cdots$, and then define $f: \mathbb{Q} \to \mathbb{Q}$ inductively and recursively. If one could define $f$ in such a way that $ \forall \ q_{n} \in \mathbb{Q} \ \exists \ c_{n} \in \mathbb{Q} : \forall \ x \in \mathbb{Q} \ |f(x)-f(q_{n})| \leq c_{n}|x-q_{n}|^2$, and $f$ is strictly increasing, we would be done. The recursive definition essentially defines $f(q_{n+1})$, after having defined $f(q_{1}),f(q_{2}),f(q_{3}), \cdots , f(q_{n})$, in such a way that these inequalities hold and $f$ is strictly increasing, and at each step the new $c_{n}$ is chosen large enough so that these inequalities do not become incompatible at subsequent steps ( I am willing to provide more details of this construction if asked).  Note that, as $n \to \infty$, we must have $c_{n} \to \infty$, so that $f$ is not uniformly differentiable. Interestingly, the only key fact about $\mathbb{Q}$ used in the construction is that it is countable, so in a sense the construction provides a proof that $\mathbb{R}$ is uncountable, given the MVT.  While the construction works, it is not very simple nor explicit, which is perhaps to be expected, and the function must be evaluated point by point in the order given by the enumeration of $\mathbb{Q}$. So I was wondering if anyone else knows or can come up with a simpler construction of a function $ f : \mathbb{Q} \to \mathbb{Q}$ such that $f'=0$ and $f$ is strictly increasing. Any thoughts and ideas are welcome.


I've created a 15.10 Ubuntu USB drive and booting off it with an ASUS Rampage IV Black Edition motherboard, I get:  Ignoring BGRT: invalid status 0 (expected 1)  and then nothing. I've become really frustrated trying to get a stable BIOS config with this motherboard (every boot produces an Overclocking failed! message and none of the even low-key default options avoid this message with an i7 3930K - this board rules as the hardest motherboard I have ever configured in the last 10 years!) and now it can't boot a vanilla 15.10 USB drive. I'd really value some help..  EDIT  I found the solution. See below.


Lie group embeddings $SO(10) \supset SU(3) \times SU(2) \times U(1)?$

Let $G$ be $SO(10)$ or $Spin(10)$.  Does either of them $G=SO(10)$ or $G=Spin(10)$ contain  $SU(3) \times SU(2) \times U(1)$ as a subgroup?  Can one show which of the following embeddings are possible rigorously: $$G\supset SU(3) \times SU(2) \times U(1)?$$ $$G \supset \frac{SU(3) \times SU(2) \times U(1)}{\mathbb{Z}_2}?$$ $$G \supset \frac{SU(3) \times SU(2) \times U(1)}{\mathbb{Z}_3}?$$ $$G \supset \frac{SU(3) \times SU(2) \times U(1)}{\mathbb{Z}_3 \times \mathbb{Z}_2}?$$  Here $\mathbb{Z}_n$ means the cyclic group of order $n$.  it looks to me that the first one is impossible, can we prove it is a no go? for $G=SO(10)$ or $G=Spin(10)$?


Linear regression: Intercept isn't significant

I built a model of multiple linear regression to predict the revenues at the box office of a movie: the variable $Y$ is revenue while the variables $X$ are two: Activity (number of tweets per day) and sentiment (connotation of these tweets).  The problem is that the intercept is not significant. I thought of a possible explanation: the intercept in practice is the value of the variable $Y$ when the variables $X$ assume values of 0; but because of the very strong development of social networks, it is virtually impossible not to have even a tweet (and then a wave of activity) about a movie that just came out, I thought that the significance or not the intercept could be neglected because the assumed value has no meaning in reality (a tweet of 0 would never be satisfied, given the market today). In this way, I consider the intercept a mere constant for the calculation of the line, without worrying about its significance (because in some cases would take negative values, which is impossible for revenues).  The interpretation may be correct?


Download a html page using url with parameters

I want to download a page from a website.  The page is located at an url like:   For download I use the code (downloaded from the internet):  function Download_HTM(const sURL, sLocalFileName:string): boolean; begin   Result:=True;   with TDownLoadURL.Create(nil) do   try     URL:=sURL;     Filename:=sLocalFileName;     try       ExecuteTarget(nil);     except       Result:=False     end;   finally     Free;   end; end;   my call is:   sURL := Format('%s/status?param1=%s&param2=%s&param3=%s',              [sWeb, param1, param2, param3]);  if Download_HTM(sURL, sLocalFile) then   ....   but don't work. Also I used:   sURL := Format('%s/status?param1=%s'#38'param2=%s'#38'param3=%s',              [sWeb, param1, param2, param3]);   but don't work. I can't insert the & character in the url. Any advice?  Now, instead of Download_HTM I tried the bellow function (from a stackoverflow example):  function GetURLAsString(const aURL: string): string; var   lHTTP: TIdHTTP; begin   lHTTP := TIdHTTP.Create(nil);   try     Result := lHTTP.Get(aURL);   finally lHTTP.Free;   end; end;   but I receive: Socket error 10014 - Bad address I'm sure that my address is corect because when I put it on the internet explorer I receive the corect html page.  When I show the sURL variable with the command ShowMessage(sURL) I can see the entire url but without the & character and the character p from the param3 word is underlined (the p character follow after the last & character from the URL) and the behavoir same to be like when I use & to create a shoertcut on a menu caption !


How do I insert the total continuation count in the allowframbreaks frame title?

I would like to change the numbering of allowframbreaks frame, for instance, from I II III to (1/3) (2/3) (3/3)， but fail to find out a command to get the total continuation count. Here is the MWE.  \documentclass[compress]{beamer} \usetheme{Warsaw}   %allowframebreaks numbering in the title \setbeamertemplate{frametitle continuation}{(\insertcontinuationcount/)} %\setbeamertemplate{frametitle continuation}{(\insertcontinuationcount/\inserttotalcontinuationcount)}  \title{title} \author{author}  %%%%% \begin{document}  \begin{frame}[allowframebreaks]{allowframebreaks title} frame 1 \framebreak  frame 2 \framebreak  frame 3 \framebreak \end{frame}  \end{document}


In Attack on Titan, it is said that titans do not have any digestive organs and the only way they get stuff out of their stomach is by puking it out.  Now, if a human is swallowed whole by the titan, will the human survive inside the titan? Yet no one is said to have survived this way.


How to run a Java Maven project from terminal

I made a Java program using IntelliJ IDEA. It's a Maven project due to I had to add the following dependencies into the pom.xml file: <dependencies>     <dependency>         <groupId>org.seleniumhq.selenium</groupId>         <artifactId>selenium-java</artifactId>         <version>2.48.2</version>     </dependency> </dependencies>  I want to run this program in the terminal but I'm a bit lost on how to do this. I tried navigating through the project folders: cd Project/target/test-classes/ Then executing this: java bot.Main But I get the following error:  Error: A JNI error has occurred, please check your installation and try again Exception in thread "main" java.lang.NoClassDefFoundError: org/openqa/selenium/WebDriver  Seems like it doesn't take into account the pom.xml file and it's dependencies, how can I properly do this? Project files are the following:  (Inside java folder (green one), there's a package named "bot" and the Main class)


Difficulty getting good ranking in Google

I have a new website that offers a collection of free sheet music. It currently has 300 pages of individual pieces of music. I am having difficulty getting the index page to rank competitively in google search results. I wonder if anyone can see something I am obviously missing? Here is the link to the index page:


Why can't the pair production process occur in empty space? I have read that a nucleus must exist and this is how it is useful: that the photon turns into virtual loops of e+ e- and one of them interacts with the field of a real charged particle exchanging enough energy and momentum so that both e+e- become real while energy and momentum are conserved in a three body diagram. What I don't understand is how the photon turns to virtual loops of e+e- what do they mean what are they... You know  there are lots of info from the Internet that now I knew them, my professor doesn't explain much, he just says that positron with a nucleus gives.... Etc so he just writes the equation but I'd really like to know specific details and it takes so much time from me.. :(


So I have my table  \begin{table} \center \begin{tabular}{| l | l | l | l |}\hline table stuff \end{tabular} \caption{Lots of words about table} \end{table}   I want it so that the caption fits to the table, kind of the same as changing the indents in Word.  Is there a way to do this?  Additionally, I have something similar to:  \newpage \subsection{NAme} TABLE STUFF INCLUDED ABOVE \subsubsection{Name}   And the table appears at the top of the page, not in between the title of the subsection and the sub subsection.  Can I change this?


Is there a way to find out where a class is used, other than attempting to delete it with Eclipse?

When I have a class I believe I no longer use, I usually attempt to delete it and see if there is an error. This strikes me as one of those things that just must be wrong...but I don't see another way. Can someone tell me what I must obviously be missing? :(


I would like to copy for backup porposes a Linux user home directory with several GBs of data and the usual configuration files. The source directory and the backup directory should exactly have the same contents. The OS is Lubuntu.  The directory contains hidden files and subdirectories. After some googling I found that  cp -r /source-directory /backup-directory   was the appropriate command.  The source directory filesystem is ext4 and the destination directory is NTFS. After the copy, diff -qr /source-directory /backup-directory gives no output (so I suppose no differences). But du, or du -b or du --apparent-size all give always different outputs for the source directory and the backup directory.  Why? Was the command wrong or is this use of du wrong?


Is there any way to see which questions have the highest views for a site?

has an insane whopping 323K views - more than many of the top-voted questions of the site.    I doubt that it's the highest-viewed question on the site itself, but I'd like to see how it stacks up against the other questions.   Is there any way to see a site's questions ranked by number of views?   I would like to see how many questions are higher-ranked in view count than mine, and by how many views they outrank my own question.


I have just learned about multivariable functions and I can't understand: $$\frac{\partial}{\partial x} \frac{\partial}{\partial y}f(x,y) =\frac{\partial}{\partial y}\frac{\partial}{\partial x}f(x,y)$$ I understand how you take the derivative of these functions, and the prof explained why they are equal but I didn't understand it too well. He wrote out the full $\frac{\partial^2}{\partial x \partial y}$ derivative using Newton's method of taking derivatives, rearranged it in some kind of way and got the other derivative $\frac{\partial^2}{\partial y \partial x}$ but at the end he said that it doesn't always work and when some limit converges the derivative exists and at that point I lost him. Do you have a good explanation for why it works?


What is Lagrangian mechanics? And how is it different from Newtonian mechanics?

I am only 15 year old,but I am terribly interested in physics. Once I was watching some kind of interesting lecture,and I came across Lagrangian-mechanics. What is it? How is it different from Newtonian mechanics? Does it "tell us" any "new" things? I would really appriciate if someone could show this to me.


In Star Wars movie, Luke blow up the death star by flying really close to the surface at high speed and shooting a missile straight down.  From what I understand it has to be at 45° before the top of the hole to shoot, like this:   <=L=>mm          m            m             m   ----------|m|---------------            |m|            |m|   Where m is the trajectory used by the missile.  Is there any explanation on how can the missile turn in such a steep way, and why couldn't it be fired from somewhere else, since the missiles seems to have extra high maneuverability ?


I'm creating a world made of cubes, similar to cube world game. Is there any quick way to create a map made of cubes that looks like this?


Is following contradictory? Can you give an example?

Is following contradictory?  "Then $f = u + iv$ is complex-differentiable at that point if and only if the partial derivatives of $u$ and $v$ satisfy the Cauchy–Riemann equations (1a) and (1b) at that point. The sole existence of partial derivatives satisfying the Cauchy–Riemann equations is not enough to ensure complex differentiability at that point."  - [1, second paragraph]  They say that $f$ is complex-differentiable iff partial derivatives of $u$ and $v$ satisfy C-R equations, but still it is not enought to ensure complex differentiability at that point.  So do you need extra conditions as wikipedia says or not for $f$ to be complex differentiability? Can you give me example, where function satisfy C-R equations, but is not Complex differentiable at certain point?


I want to change the format of a date in vb.net so I can insert it in a MySQL table.  my code:  LblDateInc.Text = Date.Today   result: 10/18/2017  in mysql table the column date need to look like this: 2017/10/18  so how to change the format of the date in vb.net or in mysql thank you


How do I remove old kernels despite 100% inode use in /usr?

I was trying to update my packages today:  $ sudo apt-get upgrade Reading package lists... Done Building dependency tree        Reading state information... Done You might want to run 'apt-get -f install' to correct these. The following packages have unmet dependencies:  linux-headers-3.16.0-44-generic : Depends: linux-headers-3.16.0-44 but it is not installed E: Unmet dependencies. Try using -f.   So, I went ahead and tried apt-get -f install:  $ sudo apt-get -f install Reading package lists... Done Building dependency tree        Reading state information... Done Correcting dependencies... Done The following extra packages will be installed:   linux-headers-3.16.0-44 The following NEW packages will be installed:   linux-headers-3.16.0-44 0 upgraded, 1 newly installed, 0 to remove and 3 not upgraded. 3 not fully installed or removed. Need to get 0 B/9,101 kB of archives. After this operation, 64.5 MB of additional disk space will be used. Do you want to continue? [Y/n] y (Reading database ... 688666 files and directories currently installed.) Preparing to unpack .../linux-headers-3.16.0-44_3.16.0-44.59_all.deb ... Unpacking linux-headers-3.16.0-44 (3.16.0-44.59) ... dpkg: error processing archive /var/cache/apt/archives/linux-headers-3.16.0-44_3.16.0-44.59_all.deb (--unpack):  unable to create `/usr/src/linux-headers-3.16.0-44/scripts/genksyms/Makefile.dpkg-new' (while processing `./usr/src/linux-headers-3.16.0-44/scripts/genksyms/Makefile'): No space left on device dpkg-deb: error: subprocess paste was killed by signal (Broken pipe) Errors were encountered while processing:  /var/cache/apt/archives/linux-headers-3.16.0-44_3.16.0-44.59_all.deb E: Sub-process /usr/bin/dpkg returned an error code (1)   It's complaining saying No space left on device. df -Th tells me that there's sufficient space:  $ df -h Filesystem      Size  Used Avail Use% Mounted on /dev/sda6       3.3G  2.5G  571M  82% / udev            2.0G     0  2.0G   0% /dev tmpfs           395M   11M  384M   3% /run tmpfs           2.0G   28M  1.9G   2% /dev/shm tmpfs           2.0G     0  2.0G   0% /sys/fs/cgroup tmpfs           100M   72K  100M   1% /run/user tmpfs           5.0M  8.0K  5.0M   1% /run/lock /dev/sda7       9.3G  7.6G  1.3G  87% /usr /dev/sda8       188G  176G  3.0G  99% /home /dev/sda1       945M  394M  487M  45% /boot /dev/sda9       256G  9.6G  233G   4% /var   However, df -i tells me /usr has used up all the inodes.  These are the dirs and their inode usage:  /usr/bin = 2846 /usr/etc = 1 /usr/games = 8 /usr/include = 3204 /usr/lib = 42317 /usr/local = 105 /usr/lost+found = 1 /usr/sbin = 306 /usr/share = 228141 /usr/src = 348704   So, if I can clear out /usr/src (which contains the current and old kernels), I can probably resolve the issue. But, I keep running into the first error:  $ sudo apt-get purge linux-image-3.8.0-35-generic  Reading package lists... Done Building dependency tree        Reading state information... Done You might want to run 'apt-get -f install' to correct these: The following packages have unmet dependencies:  linux-headers-3.16.0-44-generic : Depends: linux-headers-3.16.0-44 but it is not going to be installed  linux-image-extra-3.8.0-35-generic : Depends: linux-image-3.8.0-35-generic but it is not going to be installed E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).   Any suggestions on how I can remove my old kernels? Thanks!


Solving Fibonaccis Term Using Golden Ratio ConvergEnce

While solving , I discovered that there is a relationship between the Fibonacci sequence and the golden ratio.  After I got the correct answer via brute force, I discovered this relationship.  One of the posters said this:     The nth Fibonacci number is $[\phi^n / \sqrt{5}\;]$,  where the brackets   denote "nearest integer".       So we need $\phi^n/\sqrt{5} > 10^{999}$   $n \log(\phi) - \log{5}/2 > 999 \log(10)$   $n \log(\phi) > 999 \log(10) + \log(5)/2$   $n > (999 \log(10) + \log(5) / 2) / \log(\phi)$       A handheld calculator shows the right hand side to be 4781.8593, so   4782 is the first integer n with the desired property.   I can't quite make sense of this.  How does the poster know that the $n$-th term is $\phi^n / \sqrt{5}$?  Can you also walk me through the operations?


How do we define $\frac{\mathbb{Z}}{p\mathbb{Z}}$ for any $p\in \mathbb{N}$?

Can someone explain in simple terms, how $\mathbb{Z}/p\mathbb{Z}$ is defined as? Is it the same as $\mathbb{Z}_p$ or 'integers mod p'? If not what is the difference? Please keep it simple.


How to set PTY (Pseudo Terminal) to NON-ECHOING Unix in C / C++

I‘ve successfully implemented a PTY (Pseudo Terminal) Function: master and slave which successfully communicate. But often when I read data from the slave, it appears to be echoing. Is there any way how to disable this ? After some research I found out, that this is possible changing the flags of the termios struct: StructTermios.c_lflag = 0;  Unfortunately I didn‘t manage to disable echo in the PTY () Is there any way to do so, any ideas, suggestions, proposals, websites ... ? I would love to hear from you ❤, Regards, from Brooks (~)


How to determine whether a unique factorization domain is a principal ideal domain?

Could someone please provide an example of a unique factorization domain that is not a principal ideal domain?  Furthermore, is there some way to determine whether a UFD is a PID?


I installed eclipse via Ubuntu Software. When I start it, it take some seconds and then comes an error window showing the path of the error.  The following is the .log file:  !SESSION Wed May 02 12:53:28 BRT 2018 ------------------------------------------ !ENTRY org.eclipse.equinox.launcher 4 0 2018-05-02 12:53:28.587 !MESSAGE Exception launching the Eclipse Platform: !STACK java.lang.ClassNotFoundException: org.eclipse.core.runtime.adaptor.EclipseStarter     at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:466)     at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:566)     at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)     at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:626)     at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)     at org.eclipse.equinox.launcher.Main.run(Main.java:1438)     at org.eclipse.equinox.launcher.Main.main(Main.java:1414)   What is the problem and how can I fix it?


dhclient.conf - append to system hostname

I'm running a Raspbian on a bunch of Raspberry Pis. They each have a unique hostname set in /etc/hostname and the dhcp client correctly registers that name with my router.  The problem I'm running into stems from having these Pis connected to the same network, and then same DHCP server, via ethernet and WiFi - There is a race-like condition that means the rest of the network, when using names to address these Pis, can't deterministically prefer the ethernet connections over the WiFi.  I'd like to make the Pis report a different hostname to the network DHCP server when obtaining a lease based on which interface they connect with. This seems to be possible in a static way by adding a lines like the following to /etc/dhcp/dhclient.conf.  interface "wlan0" {   send host-name "MyHostname-1234-WiFi"; }   The problem I'm looking to solve is how to define that line programmatically. Something like this:  interface "wlan0" {   send host-name "<hostname>-WiFi"; }   Looking into the docs for dhclient.conf(5), it suggests I can use the concat function from dhcp-eval(5) but I'm not having success. I'm trying this:  interface "wlan0" {   send host-name concat(gethostname(), "-WiFi"); }


I need to run a .sh file from my Java code with out passing any arguments. I already tried doing it with  Runtime.getRuntime().exec("src/lexparser.sh");   and  ProcessBuilder pb = new ProcessBuilder("src/lexparser.sh"); Process p = pb.start();   Both of the above methods didn't work. Is there any other method to run a .sh file form Java?


How secure is the chromium browser compared to chrome?

Now that chrome has ended support for 32 bit linux, I was wondering if chromium is as secure and as reliable as chrome. If not what changes can be made to chromeium?


Early 80s sci-fi movie, cyborg(?), shooting .. had this stuck in my mind for about 30 years

This is an incredibly vague scene depiction, but I'm trying to recall a sci-fi movie I watched as a very young kid. It would have been out perhaps early 80s.  I don't recall any of the story but the image has stuck in my head and for years I always wanted to know what the movie was about. I recall a man (possibly a cyborg) who carried a shield, and for the scene I recalled drove/hovered around on something that resembled a segway or a one person standing hover craft. There was a lot of shooting going on. He may (may!) have had red infared vision like terminator (although I may just be getting that part mixed up with terminator :) I know if I saw the scene again, I'd sure to recognize it.   Anyway if anyone has the slightest inclination to what film this may be, I'd love to hear. Sorry there isn't much more I recall, I guess this is the last chance for me to put this to bed :)


How to convert a mov to a gif without loosing quality

I am trying to convert a mov I have created by recording my screen with Quicktime (I am running Mac OS El Capitan) but the result is far from perfect. I am using ffmpeg (installed using homebrew) but the end result is disappointing. Any ideas? Thank you.


Leave the door open vs Leave the door opened

Is there any subtle difference between:   We need to carry in some stuff so open the door and leave it open. We need to carry in some stuff so open the door and leave it opened.   I mean "leave it like that (in that state)".


I have to install Ubuntu on ASUS TUF GTX 1050 , but issue regarding drivers on Wimdows 10

I have a problem with drivers , cause on my Windows 10, Wifi works for a couple of minutes, then disappears, and the problem is sometimes keyboard auto types. These all issues are due to the drivers. My laptop is 9 months old. I know there isn't any hardware problem. Are the same Windows drivers installed on Ubuntu drivers or it is different?. If different. Then I, think , should install Ubuntu soon.


How do I enchant a stick with Knockback 3?

Can someone tell me how to create a knockback three stick? I searched this up everywhere on Google, but could not find any proper answers. By the way, this is for Java Edition.


I changed some settings in Unity and then I ran the Setsid unity command and now every time I try and boot up Ubuntu I can login just fine but the desktop is completely empty besides my background picture. I'm not sure how to fix it as I can't open the terminal or anything. Please help?   Thanks!


Is this Bleichenbacher '06 style signature forgery possible? (Or more like, why isn't it?)

I assume that most of you know this, but just for the sake of context; Bleichenbacher's signature forgery () basically abuses implementations that do not check that the PKCS#1 1.5 padding of a decrypted signature is correctly layed out. Most vulnerable implementations accept cases where the embedded hash is not right-justified. With a reduced padding, the hash can be moved forward (more to the left) then the remaining bytes can be treated as "garbage", which in turn make enough room for organizing so that this number is a perfect cube. In case of public exponent 3, it means that the cuberoot of the latter number is a valid signature as seen by the wrong implementation. Actually what happens is that you're basically good with the rounded cube root of a number of your choice of the form (line29, ), and cubing it only messes up the garbage digits/places anyway.  Now, I'm wondering about the case where an implementation does check that the hash is right-justified, but doesn't check the previous bytes at all. Assuming that we're still talking about exponent 3, someone could imagine that there might be a way to find a perfect cube that ends with that particular hash, thereby utilizing the more significant digits that are not checked by the code. On the other hand, the ending digits are already restricted just by the value being a cube number. Let hashlen be the length of the hash in bits, and rsalen the much bigger length of the signature. Giving up on forging a signature for a particular hash, my intuition would tell me that if you take the last hashlen bits of the possible cube numbers for the signature (for which there are possibilities on the order of 2^1/3*rsalen*) then this set would have a non-negligible intersection/overlap with the possible hash values of size hashlen. Is it possible to sign some message feasibly by somehow utilizing the structure of the particular hash in context of these (hash, perfect cube) pairs? Conversely, is there a quick and profound argument that shows that the outlined "signature checking" (looking at only the hash at the end) does not weaken the implementation?


When using SWD interface, is the reset pin necessary?

When using the SWD interface, is the reset pin is necessary?   In JTAG, there are 5 pins TCK, TMS, TDO, TDI and RST but usually SWD is a 2 wire interface. So I am confused about this.


Ubuntu 18.04 Dock mouse hover tooltips - how to disable?

I need to know if it is possible and how to disable the Ubuntu 18.04 Dock tool-tips for mouse hover the pinned application.


C++ template invalid operands of types ‘’ and ... to binary ‘operator<’

So I'm having trouble calling a template member function of a template class. When I try to do it I get the following error:  test.cpp:19:5: error: invalid operands of types ‘<unresolved overloaded function type>’ and ‘unsigned int’ to binary ‘operator<’   and clang++ says:  test.cpp:19:5: error: reference to non-static member function must be called     arrIn->partition<NPart>(NULL, NULL);     ^~~~~~~~~~~~~~~~   Any ideas how to fix this?  Thanks!  #define NULL 0  template <class V, unsigned int N> struct SubArray { public:   template <unsigned int NDIM>   void partition(const int dimsToPart[], const unsigned int numParts[]) {     // bla...   }  };  template <unsigned int N> struct CartTopology { public:   template <class V, unsigned int NArr, unsigned int NPart>   void scatterArrayBlocked(SubArray<V, NArr> *arrIn, SubArray<V, NArr> *arrOut,     const int dimsBefore[], const int dimsAfter[]) {     arrIn->partition<NPart>(NULL, NULL);   }  };  int main(int argc, char** argv) {   SubArray<int, 2> arr;   CartTopology<2> top;   top.scatterArrayBlocked<int, 2, 2>(&arr, NULL, NULL, NULL);   return 0; }


Simple Proof by induction: $9$ divides $n^3 + (n+1)^3 + (n+2)^3$

I'm trying to prove using induction that $9$ divides $n^3 + (n+1)^3 + (n+2)^3$ whenever $n$ is a non-negative integer. So far, I have:   Base case: $P(1) = (1) + (8) + (27) = 36, 36$ can be divided by $9$ so the base case is valid Inductive step: let $P(n)$ be the statement $9$ divides $n^3 + (n+1)^3 + (n+2)^3$. Assume $P(k)$ is true, so $9$ divides $k^3 + (k+1)^3 + (k+2)^3$.   And this is where I'm stuck. I'm not sure how to demonstrate that $9$ divides $P(n)$ when $n = k+1$. If someone could step me in the right direction that would be awesome. Thanks!


How can I access setter and getter methods from an instance method in a Ruby object instance?

This question is about setter and getter methods in Ruby. In the example below, I have three methods. The first two are, respectively, to get and set an instance variable @login_method. The third is an instance method that attempts to access the setter method. It fails to access the setter method, because when the line login_method = 15 is run, execution does not stop for the debugger statement I placed inside the setter method. Why can I not access the setter method from inside of method mymeth? I can access it if I prefix the setter method call with "self", but why do I have to do this?  require 'byebug' class MyClass   def login_method     debugger;     @login_method   end   def login_method=(value)     debugger;     @login_method   end   def mymeth     debugger;     login_method = 15   end end  obj = MyClass.new obj.mymeth


Is there a way to use the augmented for loop to traverse through an array where the index is also required.  For example suppose I want to traverse an array of integers and add each number along with its index to a Map. My code will be something like  Map<Integer, Integer> map = new HashMap<>();         for(int i=0; i< numbers.length; i++){             map.put(numbers[i], i);         }   Is there a way to write this using the for-each loop.


Understanding equivalence class, equivalence relation, partition

I'm having difficulty grasping a couple of set theory concepts, specifically concepts dealing with relations. Here are the ones I'm having trouble with and their definitions.  1) The collection of equivalence classes w.r.t. $R$     Def: Let $R$ be an equivalence relation in a set $X$. The collection of equivalence classes w.r.t. $R$ is the set:   $$[X]/R =\{S|(\exists x)(x\in X\land S=[x]/R)\}=\{[x]/R|x\in X\}$$   2) Partition     Def: Let $X$ be a set. A collection of sets $C$ is a partition of $X$ if:   (i) $$\bigcup_{S\in\ C} S=X.$$   (ii) $$\forall S \in C, S \neq \varnothing$$   (iii) $$\forall S, S' \in C, S' \neq S \Rightarrow S \cap S' = \varnothing$$   3) Relation induced by     Def: Let $C$ be a partition of $X$. The relation induced by $C$, denoted by $X/C$, is a relation in $X$ such that $$X/C = \{(x,y) | (\exists S \in C)(\exists x \in S \land \exists y \in S)\}$$


What are the various types of science & engineering qualifications that Batman has?

Is there any DC comic or any other authoritative source that states/lists the various science & engineering qualifications that Batman has?   EDIT:  I see that this question is on hold. However, please note that this question is not a duplicate. A question similar to this was asked previously but it did not specifically ask for the Batman's engineering & science qualifications.Consequently the answers did not address this topic( Batman's engineering & science qualifications) either.


Which word is correct for this sentence?

I don't know which one is accurate.  They all sound right to me.  The cameras need to be mounted in spots that intruders can’t reach. The cameras need to be mounted in spots where intruders can’t reach. The cameras need to be mounted in spots which intruders can’t reach.


What is the exact mechanism of flow of electricity?

When a steady current flows through a conductor, the electrons in it move with a certain average ‘drift speed’. One can calculate this drift speed of electrons for a typical copper wire carrying a small current, and it is found to be actually very small, of the order of 1 mm s-1. How is it then that an electric bulb lights up as soon as we turn the switch on? It cannot be that a current starts only when an electron from one terminal of the electric supply physically reaches the other terminal through the bulb, because the physical drift of electrons in the conducting wires is a very slow process.   What is the exact mechanism of the current flow, which takes place with a speed close to the speed of light ?


Pressure and weight? (hydrostatic paradox)

Consider two different shaped containers having same area: one is cylinder, the other is like an inverted pyramid (roughly). Both have the same level of water, the weight of the inverted pyramidal container will therefore be greater than that of the cylinder. But I know from Pascal's law that the pressure should be same in both containers. If the base areas are the same then the force (weight as measured by a scale) should also be the same. Why are the weights different?


I know I can take square root on both sides so I get z and $\sqrt{\sqrt3+3i}$ but is there a way of simplifying $\sqrt{\sqrt3+3i}$ ?  EDIT: Seems like taking the square root may not be the best thing to do (as answer suggests).


How do I show that the units of $R[x] = $ the units of $R$ where $R$ is an integral domain? I understand that given $a,b\in R$, $a$ is a unit if $a\cdot b=1$. But I'm not really sure what this means as far as $R[x]$ is concerned. I'm pretty confused so if someone can talk about any of this in simple terms, that would be awesome.


Cannot upgrade unsupported version of Skype for Linux (v5)

Skype for Linux Beta shows the following message when running the application. Is there a new version of Skype for Linux?  Sorry, this version of Skype is not supported anymore.   How can I get it work?


Practical question about usage of inheritance in php. I'm pretty new to this.  The project I'm working on encloses a.o. multiple charts which are all built up from data out of a database.  I've created multiple php classes. One class 'Filters' is inherited by all other classes. Filters connects to the DB and calculated and holds all arrays of selected filters and participants and the corresponding data.  2 classes, one class which creates the page Headers and one class which creates the Selectboxes, are used on each individual page (also inherits from Filters). And each individual page uses a class which creates a specific chart, which also inherits and uses a lot of variables from Filters. So each chart-page uses Filters + Header + Selectboxes + 'SpecificChart', the last 3 Classes inherit from Filters.  It all works perfectly. But because php does not support multiple inheritance, I created a function addFilters() to copy all necessary variables to use in the different classes, so I do not have to instantiate Filters multiple times..  I instantiate Filters and pass the object filters to the constructors of the other classes which call addFilters().  I was wondering if there's a better solution to this? Without the need to copy all the variables several times? I hope my explanation is clear..;)


Hi I am newbe in Drupal 8 and learning the new plugin system introduced in Drupal 8. I understood the concept of pluggin and also created few plugins like block and field fomatters. But I am not able to undestand the defination of pluging. Like it says     "A plugin is a small piece of functionality that may be swapped in and   out of your drupal site"   Can someone please explain (with example) the term swapped is used in context of Drupal 8.


I have got a p-value of .0166 on a hypothesis test on comparison of hourly wages for different countries. Would it be right to make a a conclusive remark that  “We can be 98.34% confident [1-.0166] that rejecting the null hypothesis and concluding that hourly wages are different for countries is the right conclusion.”


What adapter to mount a screw thread lens on Nikon D90?

I have a Soligor 450 mm lens with a 40 mm dia camera body end thread connection.  I would like to try adapting it to a D90 AF system.  Are there adapter rings available out there for this purpose?


How do I rotate a camera around the Y axis of the object it's looking at?

I'm making a camera that can currently rotate freely from the back to the front of a target object by giving it an angle and a distance.    I do the above with the following code  directionVector = new Vector3(0, Mathf.Sin (angle*Mathf.Deg2Rad), Mathf.Cos(Mathf.Deg2Rad * angle)); normalizedDirectionVector = (directionVector).normalized;  transform.position = (normalizedDirectionVector*cameraDistance) + target.transform.position;   In the above I take the direction from the angle, normalize it and then add it to the target position. And the camera sets nicely to the wanted angle. But how can I add the sideways movement(x-component) so that I could move the camera freely around the target?


How do I install pepper-flash on Chromium?

I have Chromium web browser on my Lubuntu 13.04 (pre-installed).  I use LX Terminal (pre-installed) to write commands. I am trying to download flash player on Chromium using instructions on this :  sudo add-apt-repository ppa:skunk/pepper-flash   After typing in my password, this worked. Now   sudo apt-get update   I didn't need to type in my password, as I continued on the same terminal, but got W:/ and E:/ fetch file errors  sudo apt-get install pepflashplugin-installer   I continued on the same terminal despite the fetch file errors... and they said pepflashplugin-installer could not be found.  Is the last error because of fetch file errors, or because I need to download pepflash-plugin-installer somewhere? Or is it because of something else?  I cannot download the Chrome browser, and not looking to use flash player on my Firefox web browser (installed using lubuntu software center).


The flagging page specifically states: "Something not quite right? Let us know about it."  I was flagging some items yesterday, including , which says:     The main problem I have is that there's a limit to the amount of requests I can make per minute. I've been searching on google for certain methods to use cache files to override this   I flagged it with the message:     From my understanding, this could lead to spamming of reddit. This question does not sit right with me.   It got declined because:     a moderator reviewed your flag, but found no evidence to support it   No evidence? Are you serious? He's looking to override the rate limiting on Reddit's API.


Is there any feature of asynchronous calling in PL/SQL? Suppose I am in a block of code would like to call a procedure multiple times and wouldn't bother when and what the procedure returns?  BEGIN   myProc(1,100);   myProc(101,200);   myProc(201,300);   ...   ...  END;   In the above case, I don't want my code to wait for myProc(1,100) to finish processing before executing(101,200) Thanks.


Redirecting a page after form submission

If I have a module that is creating a page, after form submission for that page, how would I redirect? Is there a function to do this in Drupal? I imagine that I would put the redirect command inside my function that executes after form submission, correct?


The inequality $\limsup \frac{c_{n+1}}{c_n} \geqslant \limsup \sqrt[n]{c_n}$

$c_n>0$ in $\mathbb{R}$, prove$$\limsup \frac{c_{n+1}}{c_n} \geqslant \limsup \sqrt[n]{c_n}$$ Tried to present $\sqrt[n]{c_n}=c_1 \frac{c_2}{c_1}...\frac{c_{n+1}}{c_n}$. Seemingly $\sqrt[n]{c_n}$ is some kind of mean of $c_1$ to  $c_{n+1}/c_{n}$. However nothing can be done...any hint?


How can I create a 3D Gaussian Distribution graph in Illustrator?

Is there a way to do this in illustrator? I suppose so, but after many tries and Google searches couldn't find a way  Tha axes don't matter, just the Gaussian distribution (the "bell" so to speak)


How were hobbits created? I can't find any reference in The Silmarillion about this. Are they just men who have shrunken over generations or what?


When I go to install, I get this error:  sudo apt-get install openssh-server    Reading  package lists... Done Building dependency tree        Reading state  information... Done Some packages could not be installed. This may  mean that you have requested an impossible situation or if you are  using the unstable distribution that some required packages have not  yet been created or been moved out of Incoming. The following  information may help to resolve the situation:   The following packages have unmet dependencies:  libxcb1 : Depends:  libxau6 but it is not going to be installed             Depends: libxdmcp6 but it is not going to be installed  openssh-server : Depends: openssh-client (= 1:5.9p1-5ubuntu1)                    Recommends: xauth but it is not going to be installed                    Recommends: ssh-import-id but it is not going to be installed E: Error, pkgProblemResolver::Resolve generated breaks, this  may be caused by held packages.   I am running Ubuntu 12.04.4  When I try to install the dependencies listed, it says I have the newest versions.


What would have been the story of the Universe if there was no mechanism to produce massive fundamental baryonic particles?

Thanks for those of you who took their time answering my problem but it seems that there is a misunderstanding between us. Most answers are based on the assumption of Electroweak symmetry breaking which was not my intent. My question belongs to an era even before this breaking took place. So, here is the edited version that it reflects my thought processes better than previous version of the question in the hope that new responses will be modified accordingly.    Let's assume that the singularity from which our Universe was created about 13.8 billion years ago (according to the Big Bang Standard cosmological model,) proceeded such that there was no need of any sort of spontaneous symmetry breaking (for any reason) to produce massive particles in early epochs. This would have created numerous massless fundamental particles. How do you think the history of our Universe would have been changed in terms of the underlying physics in large scales? In other words, if building blocks of our Universe (at least baryonic matter) were in fact all massless due to the absence of some sort of Mechanism, what would have happened to gravity? Here I truly mean before the epoch where EW and Strong interactions got separated. So, I am not talking about EW symmetry breaking but EW-Strong symmetry breaking (which happened even earlier than EW symmetry breaking such that even hadrons could not form into massive particles.) After all, we believe gravity is intertwined with spacetime fabric. What would have been the story if all the baryonic matter had started out being massless?   Somehow I thought knowing the answer for this question can guide us towards establishing a better understanding of Dark Matter and Dark Energy sectors. Maybe all the mystery lies in the fact that we have all three components interacting with each other and that's why it's too hard to make sense of everything. So, removing at least one component right from the beginning of the Universe (namely baryonic matter) should be a nice thought experiment.   Thank you for your time,


I have an HTC Inspire and I'm trying to use the new Google+ auto backup. All the photos say "Backup Failed". However, it is uploading the videos.  I have checked every setting that I know of and it looks like it is setup right.  Any ideas?


Has it been practically proven that quantum superposition exists ? If yes, how does it even work?

I was wondering if quantum particles do actually  exists in two different states simultaneously and if it has been proven they do indeed exists in a superposition of states.  How has it been figured out since observing it would collapse the wave-function into one single state (two superposition of states into one ) as it has been mentioned in the Schrodinger's cat experiment?


Recover files after accidentally formatting APFS to NTFS

I think most of these stories begin somewhat the same: I was doing X and then nothing worked anymore. In short I accidentally formatted my whole disk from APFS to NTFS. And my question: any chance of recovering my files? The device concerned is a macbook pro early 2013. While trying to install Windows 10 to the bootcamp partition I encountered a problem. Windows could not be installed to bootcamp partition with a GPT partition table. It was asking for an MBR table. Without too much thought and in an attempt to solve my problem I tried reformatting the disk. Listing the disk in window showed the correct size for the bootcamp partition. In my mind the firmware of the apple board was hiding the APFS part from windows. That explained to me why I saw no trace of it. (Probably relevant: I used the quick mode formatting.) After formatting and attempting a windows installation I was promptly greeted with a BSOD. After which I was unable to boot back into my APFS partition. Upon further inspection I noticed that the whole disk seems to be formatted as NTFS. Seeing that the windows installer started preparing the installation the GPT table might be a goner. Any chance of recovering (part) of my files? If so, what tools/methods would be safe to try? The bulk of the files can be restored from backups, but obviously I did not backup everything. And some files (pdf's, xlsx's, svg's and source code) would be really convenient to get back. I've read about TestDisk, which seems to be a good starting point. But almost all sources carry a warning about it concerning APFS compatibility. Lots of other (paying) tools seem a bit shady. I'd be open to a paying tool if I was somewhat sure it could deliver. But here again the APFS isn't helping. (Just to be clear: I'm not hoping for a full restore, just recover a few important files. Although a full recovery would be nice, but let's be realistic ...) Thank you in advance!


I am stuck with ubuntu 17.10. Is there any way I can update to ubuntu 18.04 now?

I am getting this error. How can I upgrade now?


I want to use text under an equation. I am using the \underbrace_{text{}}. My point is that the text is quite long and I want to make it into two lines. For example:  \begin{document} \begin{equation} \underbrace{1+2+3+4+5+6+7+8+9}_{\text{Aggregate \\ factor payments}}  \end{equation} \end{document}   So in my example ideally I want the "factor payments" terms to appear below the term "Aggregate". I tried in the way I have in the code, but it did not worked.   Any suggestions much appreciated


Magic: The Gathering - Does Captivating Crew's ability resolve if I bounce it in response?

My opponent has  in play.  They activate the ability to take control of one of my creatures.  In response I play  and bounce the Captivating Crew back to their hand.  Do they still gain control of my creature?


how do you pass an array to a template function?

In my main I create an object from a template class, then I call my sort method (template method)  However it get a error in my main.obj file.  error:  LNK2019: unresolved external symbol "public: void __thiscall SelectionSort<int [0]>::IterativeSort(int * const,unsigned int)" ............   Call in main:  SelectionSort<int[]> smallArraySort; smallArraySort.IterativeSort(smallArray, smallSize);   Header file: SelectionSort.h  template <class T> class SelectionSort {     public:         void IterativeSort(T data, unsigned int size);         void RecursiveSort(T data, unsigned int size);  };   sort code: SelectionSort.cpp  #include "SelectionSort.h"  template<class T> void SelectionSort<T> ::IterativeSort(T data, unsigned int size) {     int temp = data[0];     int greaterNum = 0           for (unsigned int index = 0; index < size; index++)     {         for (unsigned int inner = index; inner < size; inner++)         {             if (temp>data[inner])             {                 greaterNum = temp;                 temp = data[inner];                 data[inner] = greaterNum;              }           }     } }


As just stated in a recent  and , you can't inherit from a static class.  How does one enforce the rules that go along with static classes inside VB.NET?  Since the framework is compatible between C# and VB it would make sense that there would be a way to mark a class static, but there doesn't seem to be a way.


If you mess around with tag markup too much, the editing toolbar vanishes

I ran into  myself earlier today, the basic nature of which is that typing in certain tag markup causes the markdown preview to freeze.   I was testing this markup on Anime.SE to see what sorts of things cause errors, and at some point, I did something involving that markup - I'm not sure what, exactly - that caused the editing toolbar to vanish altogether:    Now, I have no idea how to make it reappear.   I initially caused this problem using Chrome 34.0.1847.116 on Windows 7. I tried clearing my cache (for all sites) and local storage (for ), but am still seeing this problem. That said, I don't think it's a client-side issue, because - get this - I'm also seeing the lack-of-toolbar using IE 11! This only happens when I'm logged in, though; when I'm logged-out, the editing toolbar is present and looks normal.   I also caused the same problem on meta.Anime.SE ().


Let's say I have some data, and then I fit the data with a model (a non-linear regression). Then I calculate the R-squared ($R^2$).  When R-squared is negative, what does that mean? Does that mean my model is bad? I know the range of $R^2$ can be [-1,1]. When $R^2$ is 0, what does that mean as well?


No longer able to log in to Stack Exchange

I am suddenly unable to log in to Stack Exchange. I have OpenID set up to use Google's service, and it worked perfectly for years. Now, whenever I try to log in, I see this:    The only way I was able to get back in was by following an authenticated link from one of the Stack Exchange emails (I generally frown when I see authenticated links in emails, but this time they saved my bacon :) ). Going into my profile, I see the correct Gmail account, and I was even able to add a secondary one:    However, if I try to log back in, I still get the "new to Stack Exchange" message.   I also tried using password recovery - but that is also impossible, even though I'm using the same email:    Why does this happen, and what I can do to log in "normally" once again?


Can the Wish spell be used to increase ability scores?

Could you wish for an ability score of 30 in D&D?


ArrayList.remove() is not removing the ArrayList element as expected

New Java learner here, working on Codecademy practices. I want to remove "ant" from an ArrayList, but my code doesn't remove it.     for(int i=0;i<lunchBox.size();i++){      if(lunchBox.get(i)=="ant"){        lunchBox.remove(i);  I looked at the solution and it shows     if (lunchBox.get(i) == "ant"){ lunchBox.remove(lunchBox.get(i)); i--;   I've read a little on the .remove() method but I can't seem to understand why my code won't remove that element. Thanks!


Where is the error in this "proof" that 3=0?

I saw  (link at bottom), with a supposed "proof" that $3=0$. It goes as follows:  Let $x$ be a solution of $$x^2+x+1=0 \tag1$$  Since $x\neq0$, we can divide both sides by $x$: $$\frac{x^2+x+1}{x}=\frac0x\implies x+1+\frac1x=0 \tag2$$  From $(1)$, $$x^2+x+1=0\implies x+1=-x^2$$  Substitute $x+1=-x^2$ into $(2)$ $$\begin{align*} -x^2+\frac1x&=0 \tag3\\ \frac1x&=x^2\\ 1&=x^3\implies x=1 \tag4 \end{align*}$$ Substitute $x=1$ into $(1)$ $$\begin{align*} 1^2+1+1&=0\\ 3&=0 \end{align*}$$  The explanation given in the video is  Substituting $x+1=-x^2$ into $(2)$ creates the extraneous solution $x=1$ which is not a solution to the original equation $(1)$, $x^2+x+1=0$.  Equations $(1)$ and $(2)$ have solutions $\frac{-1\pm i\sqrt3}{2}$, but after the substitution, equation $(3)$ has these two solutions and $1$.  Basically, it is saying that the issue is substituting $x+1=-x^2$, but I'm not sure if this is actually the problem. How can a substitution cause an issue if everything before the substitution is correct? After reading the comments, I realised many of them say that the real issue is $(4)$, because $1=x^3$ could also mean that $x=\frac{-1\pm i\sqrt3}{2}$. Not considering these solutions is the issue with the "proof". One also needs to check these solutions before making conclusions, and "pick" whichever one is correct. So, my question is, what is the issue with the above "proof" that $3=0$?  Video: "Prove" 3 = 0. Can You Spot The Mistake? .


I just completed writing my first program in python, i have written all my functions in a single module, i just executed it from command line by giving the input files as argument and it worked. But when i gave a big dataset, my program continuously running for some time. Now my next step is to find which function is taking more time in my module. I could get the time taken by whole program, but i need for each function separately.  I tried to understand timeit and profile modules in python, but as per my understanding, they were giving the time taken by a particular function. Is there a way to know the time taken by each function in my module as a statistics( all at once )?  Thanks in advance.


Emptying a file for root user does not work

I use below command to empty a file  > file.txt   It works perfectly fine! But there are some files with root user permissions. So I tried   sudo > different-file.txt   and I got below verbose  usage: sudo [-D level] -h | -K | -k | -V usage: sudo -v [-AknS] [-D level] [-g groupname|#gid] [-p prompt] [-u user name|#uid] usage: sudo -l[l] [-AknS] [-D level] [-g groupname|#gid] [-p prompt] [-U user name] [-u user name|#uid] [-g groupname|#gid] [command] usage: sudo [-AbEHknPS] [-C fd] [-D level] [-g groupname|#gid] [-p prompt] [-u user name|#uid] [-g groupname|#gid] [VAR=value] [-i|-s]         [<command>] usage: sudo -e [-AknS] [-C fd] [-D level] [-g groupname|#gid] [-p prompt] [-u user name|#uid] file ...   This suggests that there is some syntax error in my command.  What is wrong?


For example, given the following code, when I first click the parent and then click the child element, the events always seem to fire in this order MOUSEDOWN, FOCUSOUT, FOCUSIN:  html  <div  id="parent"  tabindex="0"  style="background-color: blue; height: 100px; width: 100px;">  <div    id="child"    tabindex="0"    style="background-color: red; height: 50px; width: 50px;">  </div> </div>   js  var node = document.getElementById('parent');  node.addEventListener('mousedown', function () {  console.log("MOUSEDOWN"); });  node.addEventListener('focusin', function () {  console.log("FOCUSIN"); });  node.addEventListener('focusout', function () {  console.log("FOCUSOUT"); });   This appears to be true for IE11 as well. Is this just an implementation coincidence or is there an officially defined order event listeners for each event type will be triggered in? Can I rely on mousedown always coming before focusin or focusout?


$1+a$ and $1-a$ in a ring are invertible if $a$ is nilpotent

Let $(A, +, \cdot)$ be a ring with $1$.  An element $a\in A$ is nilpotent if there exists $n\in \mathbb{N}$ so that $a^n=0$.      Show that if $a$ is nilpotent then $1+a$ and $1-a$ are invertible.


Why don't I appear in the Stack Overflow ranking?

I have a reputation of over 300 on Stack Overflow. I was searching my name in the Stack Overflow ranking () to look up my position. But it doesn't appear.   Question:  Is there another condition that I must meet to be in the ranking?


In a proof by contradiction, what if both the proposition and its negation lead to contradictions?

I'm learning math.  I've recently thought more about the proof by contradiction technique, and I have a question that I would like cleared up. Let me set the stage.  Suppose I am trying to prove a theorem.  Theorem: If A and $\neg$B, then $\neg$C.  Proof (contradiction): Let us suppose that A is true and $\neg$B is true. Let us assume that C is true ($\neg$C is false).  [blah blah blah]  From this, we arrive at a contradiction because we see that B is true ($\neg$B is false), but we know that $\neg$B is true (because we assumed it to be true). Thus, since assuming that C is true lead us to a contradiction, it must be the case that C is false ($\neg$C is true). QED.  My issue with this: why is it that C leading to a contradiction must mean that $\neg$C is true? What if $\neg$C also leads to a contradiction? In that case, doesn't a proof by contradiction not prove anything? Why can we be sure that C leading to a contradiction must mean that $\neg$C doesn't lead to a contradiction?  I'm sorry if this question has already been asked. I searched for a bit before asking to see if anyone had this same specific question, but most results just asked why a proof by contradiction works in general without any clear question.


Declaring an Array in Java with a Generic Type

Please consider the following code:  public class A<T> {       public void main(String[] args) {         A<String>[] array = new A<String>[10];         System.out.println(array.length);     } }   I am trying to define (and allocate space for it) an array of 10 elements where each element of the array is of type A. I thought the above code would do it, but it fails to compile.  Thanks, Bob


Currently, I'm attempting to make multiple beziers have equidistant points.  I'm currently using cubic interpolation to find the points, but because the way beziers work some areas are more dense than others and proving gross for texture mapping because of the variable distance.  Is there a way to find points on a bezier by distance rather than by percentage?  Furthermore, is it possible to extend this to multiple connected curves?


Do LTS releases get the newest program versions?

New versions of programs can sometimes be found in the official packages of newer Ubuntu releases.   For example, the DAE-software Asunder gets installed in version 2.8-3 in 16.04, while the most current, fully-updated version in 15.04 is still 2.7-2.  Is this because 15.10 will lose support in a few weeks or do LTS releases also not always receive the newest versions of featured programs? If not, is it possible to update the newer packages somehow?


Precise rules of variable binding in nested scopes

I seem to have misunderstood something about Python variable binding. What are the precise rules for deciding which variable is accessed given a nested scope with shadowing names? Let me illustrate with some examples. First the basic shadow. a = 1  def foo():     a = 2     def _foo():         return a     return _foo()  print(foo())  # -> 2  Everything is fine here. The value is overwritten and returned accordingly. However, if the value is changed after the function definition, it is still the inner value: def bar():     def _bar():         return a     a = 2     return _bar()  print(bar())  # -> 2  What's more, defining a function that references a non-existent variable is possible. def baz():     def _baz():         return b     return _baz()  Then, if b is defined later, the function can be executed. But not if is defined in another inner scope: def qux(f):     b = 3     return f()  print(qux(baz()))  # -> NameError  Now all of these cases could be explained by having Python know about lines that come later in the program, but that conflicts with my knowledge of Python being an interpreted language, advancing line by line. So are statements parsed at once instead of line by line? A weird behaviour with shadowing class attributes throws me off a bit more. class C:     a = 2     b = a      def meth(self):         return a      c = meth  print(C.b, C().meth(), C.c)  # -> 2 1 C.meth  Here a is defined as a class attribute and is successfully used in b, but this does not carry over to the method definition. The method itself can be used in later attributes, but not for example in other methods without going through self. Is my guess about the binding happening all at once correct? And in that case are class bodies an exception by design, or are they not a scope at all? Or is something else going on here?


How can I avoid SSH's host verification for known hosts?

I get the following prompt everytime I try to connect a server using SSH. I type "yes", but is there a way to aovid this?  The authenticity of host '111.222.333.444 (111.222.333.444)' can't be established. RSA key fingerprint is f3:cf:58:ae:71:0b:c8:04:6f:34:a3:b2:e4:1e:0c:8b. Are you sure you want to continue connecting (yes/no)?


Java if Statement under enhanced for loop did not work

This is a code fragment that I am working with for a logon system using hashset Users. I checked the enhanced for loop part it works but the if statement seems like it never works out, even if the values are equal.  if (comm.equals("Sign in")) {     user urs = new user(p_name, p_pass, p_id );      Iterator<user> iter = Users.iterator();     for(user obj : Users) {         if (p_u == obj.getUsername()&& p_pw == obj.getPassword ()&& p_sn== obj.getStudentID()) {             JOptionPane.showConfirmDialog(                 jf,                  "Success", "Success",                 JOptionPane.DEFAULT_OPTION);             break;         } else {             log_in.setText("Try Again");             exit.setText("Create User");          }


What is the curvature of an empty universe?

My calculations tell me an empty universe has hyperbolic curvature. Is this correct? If it is, can anyone help me understand why this is intuitively?


I am attempting to add a user but the terminal seems to crash

I'm trying to add a user using: sudo -s adduser leslie  I get this result: [sudo] password for david:   From then on I type but nothing appears. I need to setup the Sharing preferences. I'm using Ubuntu 15.04.


Filling in Null Data Gaps in Raster Image

I am looking to fill in small gaps of no data/null values in my raster image within ArcMap.   Are there any good techniques to approach this, while also not degrading the image in the process?


Why the $(n+1)$th prime number cannot exceed the smallest prime divisor of $p_1\dotsc p_n + 1$

Let $p_n$ be the $n$th prime number in its natural order. We want to show that  $$p_{n+1} \leq p_1\dotsc p_n + 1 \tag{1}$$  I know $p_1\dotsc p_n + 1 > 1$, so it has at least one prime divisor, but the text says that $p_{n+1}$ cannot exceed the smallest of these divisors, but I cannot understand why, especially when I imagine $p_{n+1}$ being very large. Although some examples confirm that this statement is true, I cannot make a connection as to why the $n+1$ prime number cannot exceed the smallest prime divisor. Once this has been shown to be true, $(1)$ immediately follows.


Doing two PhDs one from Electrical Engineering and other from Theoretical Physics

I am currently doing MPhil degree in Electrical Engineering (Sensors & Robotics). I did my bachelor degree in Electrical Engineering as well.  I have real motivation and love to do research on Theoretical Physics as well. The more I learn physics more I need to do a research on physics.  My initial thought was to get an M.Phil on the current University in EE and get my Ph.D. in Electrical Engineering from some other more reputed university. But since now I have an idea of doing Ph.D. in physics, now I am thinking of extending my M.Phil to a Ph.D. and finish it and do another Ph.D. on physics in a foreign University (Australia).  I have two questions, 1)what is your opinion on this path? I appreciate answers, especially by PhD supervisors. 2) Does getting a Ph.D. in electrical engineering minimize my chances of getting selected for a PhD( funded Ph.D.) in theoretical physics? (I mean is it better to apply for Ph.D. in theoretical physics after completion of just M.Phil).  Note: It takes only one extra year for Ph.D. if I extend my M.Phil.


Is one preposition enough for multiple months?

A colleague of mine has written her thesis and requested me to read and correct its grammar. I have seen some sentences like     The maximum deviation of the concentration values were obtained in the growing season, especially in May, in July, in August and in September.   As you see there is one 'in' for each month. I think that one preposition would be enough for all:     The maximum deviation of the concentration values were obtained in the growing season, especially in May, July, August and September.   Which one is more suitable?


Stop and Start a service via batch or cmd file?

How can I script a bat or cmd to stop and start a service reliably with error checking (or let me know that it wasn't successful for whatever reason)?


Polarization of light using QM principles

If we have vertical linearly polarized light and if we put it through a polarizing filter oriented at 45 to the vertical, then only half of the light passes through.   I am able to intuitively grasp this fact as photons of vertically polarized light may exist in a superposition of being in two diagonally polarized and mutually perpendicular states, for which the amplitudes interfere. Thus upon interacting with the filter half of the photons pass through.   But if we subsequently pass this light through another filter which is oriented horizontally, still half of this light will pass through.   Why does this happen? Doesn't the fact that it passed through the first filter mean that it is oriented diagonally without uncertainty? How can it, after passing through the first filter, still exist in superposition of two states? Wouldn't the act of passing it through a filter disturb this superposition and force it to occupy one definite state?


Cycles per byte seems to be a critical concern in designing and choosing stream ciphers. For example, from Wikipedia, RC4 has 7 cycles/byte on original Pentium chips.  How is this calculated? Do they just time the encryption of multiple megabytes and then divide by the CPU's clock speed? Do they look at the assembly code and lookup cycle per instruction in some table, figuring in pipelining, branch prediction, etc.?


$z$ is a complex number. What does $2|z+3i|=|z-i|$ represent?  Putting $z=x+iy$, I get a circle with radius $\frac83$. But the equation of circle is $|z-z_1|=r$. How to intuitively see that $2|z+3i|=|z-i|$ represents a circle?


I dropped my cpu chip about 8 cm, at most, but unfortunately it fell on the corner. Four pins are bent. The worst is bent perhaps to 70 degrees, at most. None of the pins contact other pins, and the chip still fits into the socket with the arm going down effortlessly. The bent pins are at the bottom of the same line of pins that has the alignment arrow, in case that means something to someone. I am reading that some are just ground pins. Wouldn't that be lucky if it were the case for me? Anyway, should I try to straighten these, or is it likely to work just as it normally would? I feel like I should choose before putting paste on it an attaching the fan as I've never actually taken a cpu out after installing it on a motherboard. I imagine it would be hard to detach it from the fan and would prefer not to go there. Edit: Well, I went ahead and did it with a medium thin sewing needle. It is thin enough to fit between the corner pins, and just the slightest bit of prying moved them. They are very delicate. I do feel better about how it fits in there, and there is a much more quiet tiny noise when I put the arm down now. It did fit before, but it had just the slightest lateral give, and that made me uncomfortable. Is it possible that I could have damaged it by scratching it, by getting oil from my skin on it or by blowing on it? If yes, how should I check to make sure it is working fine?


When I boot Ubuntu 18.04 it's not getting to the GUI interface. It's booting to a black screen with this error message.  /dev/sda5 contains a file system with errors, check forced. /dev/sda5: Inodes that were part of a corrupted orphan linked list found.  /dev/sda5: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.         (i.e., without -a or -p options) fsck exited with status code 4 The root filesystem on /dev/sda5 requires a manual fsck  Busybox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3.2) built in shell (ash) Enter 'help' for a list of built-in commands.  (initramfs) _


In reported speech, tenses are generally backshifted. If what was said is still true at the time of reporting then back shifting is optional.  My question is, if someone doesn't backshift the tense knowing for a fact that the statement is no longer true, is that still acceptable?  For example, suppose John tells me today:      I am hungry.    Then two days later, I happen to tell my friend:        John said that he is hungry.   Even though I know that John is no longer hungry, I used the present simple tense (is). Is this usage correct?


Is inversion correct after "I asked how old..."?

Being curious about the tractor, I asked how old is that tractor?                                             Being curious about the tractor, I asked how old that tractor is?   The grammar checker that I used stated that the first sentence shown above is wrong (looks OK to me). I re-worded the sentence as shown in the 2nd sentence, and my grammar checker then approved the 2nd sentence shown above.  Here is what my grammar checker had to say about the 1st sentence:      It appears that the verb and noun phrases "is that tractor" are incorrectly inverted. Consider changing the word order.                                                       Which of these two sentences uses the correct word order, and why?


def random_bitstring_generator(bit_number, backend):           bitstring = ""      one_qubit_random_bit_generator_circuit = QuantumCircuit(4,4)     one_qubit_random_bit_generator_circuit.h(3)     one_qubit_random_bit_generator_circuit.measure(3,3)      for _ in range(bit_number):         counts = execute(one_qubit_random_bit_generator_circuit, backend, shots=8000).result().get_counts()         bit = list(counts.keys())[0]           bitstring += bit      return bitstring  from qiskit.providers.aer import QasmSimulator  provider = IBMQ.load_account() ibmq_melbourne = provider.get_backend('ibmq_16_melbourne') backend = QasmSimulator.from_backend(ibmq_melbourne)  print(random_bitstring_generator(512, backend))```  Using the above  code, I am only getting an output bit string with all 0's even with changing number of shots. what is the error leading to incorrect output. I am trying to generate a long random sequence


This is part of a bigger exercise.   I am stuck on evaluating. $\sum_{k=2}^\infty \frac{k}{3^k}$   Though have done all the rest of the task..   If you calculate it on wolfram you will find out that: $\sum_{k=1}^\infty \frac{k}{3^k} = \frac{3}{4}$ But why? I need to prove it by hand. I thought about writing it as a cauchy product but i think it is impossible.


"I think him to be about 50" or "I think he is about 50"?

I have two options. Which one is correct?      a) I think him to be about 50.   b) I think he is about 50.   If both are correct, should I avoid one or the other?


How do I align enumerate items inside empty description?

I have an enumerate list inside an empty description item. The minimal file is, \documentclass[11pt]{article}   \begin{document} \begin{description} \item [A Label:]    \begin{enumerate}   \item A1.   \item A2.   \item A3.   \end{enumerate} \end{description}    \end{document}  The problem is, A1 comes after the colon (:). As you can see here,  But I want A1 in a new line, with 1. aligned with 2. I tried putting a \relax in the empty description item. Nothing was improved. Any suggestion will be appreciated.


Postgresql wont start after reboot. Kali linux Raspberry Pi 2

I have been trying for days to get postgresql to work and it did briefly before a restart. How to I set the correct permissions? This is the error I get when I try to start the service after a reboot.  root@kali:~# service postgresql start [....] Starting PostgreSQL 9.1 database server: main[....] The PostgreSQL server failed to start. Please check the log output:  2015-05-24 08:51:21 UTC LOG: database system was interrupted; last known up at 2015-05-24 07:33:08 UTC  2015-05-24 08:51:22 UTC FATAL: could not open file "/etc/ssl/certs/ssl-cert-snakeoil.pem": Permission denied  2015-05-24 08:51:22 UTC LOG: startup process (PID 2505) exited with exit code 1  2[FAIL5-24 08:51:22 UTC LOG: aborting startup due to startup process failure ... failed!  failed!   I have read all the related posts on the subject, they didn’t solve my problem, so it's different. I don’t know exactly how, I can provide any extra info that is required.


How to solve collinearity problems in OLS regression?

Please see the model below (). The independent variables are properties of 2500 companies from 32 countries, trying to explain companies' CSR (corporate social responsibility) score.   I am worried about the VIF scores of especially the LAW_, GCI_ and HOF_ variables but I really need them all included in the model to connect it to the theoretical background the model is built upon. All variables are discrete numeric values, except the law LAW_ variables: they are dummies as to which legal system applies in the companies' country of origin (either english, french, german or scandinavian).    Amongst other articles, I have read  about dealing with collinearity. Often-suggested tips are removing the variable with highest VIF-score (in my model this would be LAW_ENG). But then other VIF-scores increase as a result. I do not have the proper knowledge to see through what is going on here and how I can solve this problem.   I have uploaded the corresponding data  (in SPSS .sav format). I would really appreciate somebody with more experience having a quick look and tell me a way to solve the collinearity problem without taking out (any or too many) variables.  Any help is greatly appreciated.  P.S. For reference, I am including a correlation table ():


I am using Mac OS X 10.9.4, following is my script to copy files from local machine to different host  #!/bin/bash #!/usr/bin/expect  echo "I will fail if you give junk values!!" echo " " echo "Enter file name: " read filePath echo " " echo "Where you want to copy?" echo "Enter" echo "1. if Host1" echo "2. if Host2" echo "3. if Host3" read choice echo " " if [ $choice -eq "1" ] then   spawn scp filePath uname@host1:/usr/tmp      expect "password"      send "MyPassword\r"   interact elif [ $choice -eq "2" ] then   spawn scp filePath uname@host2:/usr/tmp      expect "password"      send "MyPassword\r"   interact elif [ $choice -eq "3" ] then   spawn scp filePath uname@host3:/usr/tmp      expect "password"      send "MyPassword\r"   interact else   echo "Wrong input" fi   when running this script i am getting following  ./rcopy.sh: line 21: spawn: command not found couldn't read file "password": no such file or directory ./rcopy.sh: line 23: send: command not found ./rcopy.sh: line 24: interact: command not found


How to exclude a field when a search is done?

I just enable the Search Form (provide by the search module) block to allow the visitor to make searches.  When a search is done the entered word is searched in all field of the nodes.    Can I exclude a field?  Let's say the content type has the fields: title, body and provider.  Then when a search is done I need to exclude the field provider from the search.  I have the custom_search module enabled but I see no way to exclude fields.


What is the Topology of Cantor set as the subset of real line with standard euclidean topology?

It may be an odd question.  But, I particularly want to know the open's of cantor set with inherited topology of real line.


PC boots into GRUB console after Windows update

Yesterday I had to boot into Windows and when shutting down again Windows wanted to install updates (which is why I switched to Ubuntu in the first place).  Today I booted my PC and I get this screen:    Now I don't know what to do. Normally this is where the screen comes that lets me choose between Ubuntu 18.10 and the Windows Boot Manager.


Can I type accented characters (é, ř, ...) in Windows by holding a key (like on Android)?

Is there a way to set up Microsoft Windows so you can enter accented characters (with diacritics, such as é, ř, ...) by holding a key and then selecting the variant you like? I mean a similar way like on tablets and mobile phones.  E.g. you hold the key E and instead of auto-repeating the same character the system would offer you a small menu on the position of the cursor offering É, È, Ê etc.  Note: I am aware of other ways to enter accented characters. This question is purely about this particular typing method and if it is possible to set up on Microsoft Windows. Maybe using a 3rd party software?


Is "until juices run clear" a valid test for poultry doneness? Why or why not?

I've come across this particular recommendation many times in  and cookbooks and probably even given it out myself once or twice.  Poultry is sufficiently cooked when the juices run clear, not red or pink.  In recent months and years, as I've grown more interested in and knowledgeable about the science of cooking, I've learned to be skeptical of such simplistic claims.  This one is repeated everywhere - even the  says it - but I've also run across various .  What I'd like to know is this:  What does it actually mean - chemically or biologically speaking - when poultry juices run clear?  Is it actually a reliable indicator that the food is safe to eat?  P.S. I am quite well aware that the way one is supposed to test for doneness is to use a thermometer and ensure that the internal temperature has reached 165° F / 74° C.  I always do this, but thermometers can break, run out of battery, etc., so I think it is still helpful to know if the juice test is ever a viable alternative.  But most importantly I am interested in understanding what is happening to the meat that causes the juices to change colour, and under what other conditions this can happen.


In a Javascript ternary operator, can you loop through an array?

I have a ternary operator which sees if values in an array are the same as my targeted value. Is there an easy way to do what I'm trying to do to save me a lot of time and hard coding in array indexes. Is there a way to not use a lot of or operator?  I essentially have a long list of array indexes to compare against like this:  (price[0] === this.props.result.cost ||  price[1] === this.props.result.cost ||  price[2] === this.props.result.cost ||  price[3] === this.props.result.cost ||  price[4] === this.props.result.cost )  ? this  : that   I feel like there is something basic that I'm missing or some other way completely to make this an easier task to do.


I have been trying to do Principal Component Analysis (PCA) via R.  The data set is available at   I tried to do PCA via 2 different methods -    prcomp princomp   I have used correlation matrix as all the variables are on different scales. Whilst, I can understand a slight difference, there appears to be a major difference between the two. I have illustrated the same below -     car <- read.csv("D:/Cars.csv")        car <- car[,c(2:7)]        pc <- princomp(car, score=TRUE, cor=TRUE)        pca <- prcomp(car, score=TRUE, cor=TRUE)        summary(pca); summary(pc)   The result of the above is -     We can see the summary of the prcomp method above and the princomp method below. As visible, both are extremely different : in the sdev as well as the proportion of variance. Further, their respective components are also vastly different, as is visible below -   prcomp is above and princomp is below in the pic, once again. Can somebody please explain as to why there is such a huge difference between the two ? Also, are these two methods the correct ones to perform PCA or should I go ahead with a different method (e.g. PCA() )  Thanks in advance :)


Find infinitely many integral solutions $(x^2+x+1)(y^2+y+1)=z^2 +z+1 $  My assumption: $(x=y=z=0), (x=z, y=0) (x=0, y=z)$. Is there any other way to find. If so, please help me to proceed. Thanks in advance.


Turning off dashed lines on object imported from sketchup

I've begun importing from sketchup and my model groups have wire ( dashed line ) going back to the datum origin. They don't show in final renders  but is there any way I can turn off their displaying as they get in the way?    this is the same no matter if I use Blendup, but its the same via Collada, and 3DS.


What's the point of putting two NOT gates sequentially?

I found the following diagram in data sheet for M74HC595 8 bit shift register   I have three questions.   Do I understand correctly that all blocks inside red ellipses are NOT gates? What is the difference between (circle-triangle) and (triangle-circle) symbols? Why did they put two NOT gates sequentially? These two gates will just pass through unchanged input signal according to NOT truth table. Will the circuit without these two NOTs operate the same way?


How can the integrity of Debian's debian-keyring package be verified?

I encountered a Debian machine that, when trying to update packages, threw the widely discussed "GPG error:  wheezy/updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553". In oder to import the current keys, the package debian-keyring needs to be installed.  But since the keys on the machine are no longer valid, how can I be sure that the packet's contents have not been tampered with?


In quantum mechanics and gravity theories one always meets the word "singularity" in connection with talks about black holes and the big bang, etc. Now in mathematics a singularity is well defined – mostly as a pole of $n$-th order that makes the function value approach infinity near the singular point...  But I cannot imagine that a singularity can actually exist in the real world. It is simply "un-physical" and any equations having physical meaningful singularities must be wrong or the singularity somehow excluded just like saying $v/c$ is always less than 1.  Hence, a black hole can not in it self "be" a singularity but might behave as such near that point, which, however, nothing ever reaches. Thus it can not be observed and is physically non-existent as a point in time and space but only an abstraction – similar to what I would be tempted to say about the photon.


In recent years, people build huge neural networks with millions of parameters to learn.  I have seen many discussions about gradient based training, but not too much for Newton's Method / Quasi Newton Method.   Is that true Newton's Method / Quasi Newton Method are not widely used in deep neutral network training?   Is this because the Hessian is too large, so even an approximation of that such as BFGS would not work? But the gradient can be weakly approximated in different way?  Any review papers about the optimization methods used in deep learning neural network?


I'm reading Robinson Crusoe and came across many of these constructions with "but" in it. I can't help but thought they were a little unusual. I don't consider myself fluent in English, that's why I ask.  Here is an example:     This I saw no remedy for but by making an enclosure about it with a   hedge; which I did with a great deal of toil, and more, because it   required speed.   Second one:      However, as my arable land was but small, suited to my crop, I got   it totally well fenced in about three weeks' time;   By typing the second out I figured it is actually the normal textbook case of "but", just an, in my opinion, screwed ordering in the sentence. Is this what it means?     However, as my arable land was suited to my crop but small, I got it   totally well fenced in about three weeks time;   Why did the author do this? Can you comment on the first sentence too? It's not a textbook-but-usage as I see it.


What does Superman see while using his heat vision?

I've always wanted to know if he can see while he's using his heat vision, and if he can, what does it look like, is everything red, does his vision spectrum change?   Have we ever seen through his eyes while he was using his heat vision?


Printer not recognized on Ubuntu Libre Office

I am running 14.04 and have a HP Deskjet 2545 wireless printer which is supported by Ubuntu. I have run HpLIP, the latest version and installed the printer.  The printer is recognised by Ubuntu, printer and network, but LibreOffice do not see the printer. Only a Generic printer.  I don't know what to do anymore and would like to get some good advice


Python lxml cant navigate when using namespace

I have a python script that is reading in an xml file using lxml.  However lxml is getting thrown off by the namespace.    Ie if delete xmlns="http://theurl.com" from my xml file before running the script it works fine and finds all the elements.  I am really struggling on how to modify the script to make it so I dont need to delete the name space reference from the xml file before parsing.   Sample Code  from lxml import etree root = etree.parse(r'myfile.xml')  Elements=[] for elements in root.xpath('//element'):       print(list(elements.keys()))   Sample File.    <ServiceDefinition xmlns="http://theurl.com" " version="1.0.1.0">       <schema>          <seqtype="xyz">             <element name="element 1"/>             <element name="element 2"/>          </seqtype>        </schema> </ServiceDefinition>


Is "they" plural or singular when it's someone's preferred pronoun?

Andy's preferred pronoun is "they". They goes to school in Denver, where they studies philosophy.   or      Andy's preferred pronoun is "they". They go to school in Denver, where they study philosophy.   Also, should Andy refer to himself as "I" or "we"?


How can I find out which packages take up the most space after installation, and their dependencies, so I can decide which to remove?

The end goal is reduce the footprint that apps and their dependencies use. To that end, we need to know the sizes of packages and their dependencies.   Unfortunately as any experienced Linux user will tell you, there is no safe way to automatically remove dependencies i.e., through a script. Inevitably if you do this you will break something. So you have to go about it manually.   Hence the user needs some way to find out what is taking up disk space because mere package size is insufficient. I have scoured the web looking for a command to provide this information but did not find one, so I constructed my own.


So I went to my biometric appointment and I have all my paperwork set up. I bought my shipping label on the VFS website and now I am trying to unlock it through the confirmation email. I type in the correct password and it denies me. I have called the UK, I have emailed VFS but they take 2 days to respond. Has anyone had this issue? What did you do?


How to make a table like this? I have tried many ways to do it but all are failed. I am so confused. Thank you so much for any reply.


Python declare variables only the first time I call a function

I have a function in python and I want to declare 2 variables only the first time I call this function and then change their values, something like this :  def function():   x=0   z=2   if(x>z):     other_function()   else:     x+=1   With this way,every time I call the function(), x becomes 0 and z becomes 2.   I tried to make them global outside of the function() but it gives me error :      UnboundLocalError: local variable 'x' referenced before assignment   How can I declare the values the first time I call the function()?


jQuery cannot find input by ID which was dynamically added

I have a select input in which the options are 1-6. Depending on the value of that, the same number of inputs are appended to an empty div with unique Id's as such: $('#no_of_children').change(function() {     let inputContainer = $('#children_inputs');      console.log(inputContainer);     inputContainer.empty();      let num = $(this).val();     console.log(num);      for(let i = 1; i<=num; i++) {       inputContainer.append("
Child "+i+". Age: <input class='form-control' type='date' name='child' id='child"+i+"'>
");     }   });  What I expect to happen afterwards is to be able to use $('#child(n)') to get the the input (n being whatever number 1-6). When I inspect the element I see that the inputs are there with the correct ID, but the jQuery selector cannot find it. I have also tried: $('#child1').on('change', function() {     console.log("changed");   })  which was recommended when I researched this problem but it does not work for me.


Algebraic identity arising from coupon collectors problem.

Prove the following identity:  $$\sum\limits_{k=1}^{n} (-1)^{k+1}\frac{n \choose k}{k}= 1+\frac 1 2 + \frac 1 3 + \dots \frac 1 n \tag{1}$$  EDIT: Equation (1) above is proved via integration by @donaldsplutterwit. And I suppose this could lead to the equivalent identity below. However, still want to see if there is a more direct way to prove it.  Or equivalently, prove that when $n$ is even (see my attempt for why equivalent):  $$\sum\limits_{k=1}^{n-1}-1^{k+1}\frac{n-1 \choose k}{n-k} = \frac 2 n$$    My attempt:  I denote $S_n$ as the LHS of equation (1) and try to show $S_n-S_{n-1}=\frac 1 n$  Let   $$S_n = \sum\limits_{k=1}^{n}(-1)^{k+1}\frac{{n \choose k}}{k} = \sum\limits_{k=1}^{n-1}(-1)^{k+1}\frac{{n \choose k}}{k}+\frac{-1^{n+1}}{n}\tag{2}$$  Now,   $${n \choose k} = \frac{n}{n-k} {n-1 \choose k} = \left(1+\frac{k}{n-k}\right){n-1\choose k}$$  Substituting into equation (2):  $$S_n = S_{n-1} + \sum\limits_{k=1}^{n-1}(-1)^{k+1}\frac{{n-1 \choose k}}{n-k}+\frac{-1^{n+1}}{n}$$  We require: $$S_n-S_{n-1} = \sum\limits_{k=1}^{n-1}(-1)^{k+1}\frac{{n-1 \choose k}}{n-k}+\frac{-1^{n+1}}{n}=\frac1 n$$  This would imply:  $$\sum\limits_{k=1}^{n-1}(-1)^{k+1}\frac{{n-1 \choose k}}{n-k} = \begin{cases}\frac2 n, & n\%2=0\\     0,    & n\%2=1\end{cases}$$  The second case is easy to see since if $n$ is odd, the $k$ th term of the summation above becomes:  $$t_k = -1^{k+1}\frac{n-1 \choose k}{n-k}=-1^{k+1}\frac{(n-1)!}{k!(n-k)!}$$  And  $$t_{n-k} = -1^{n-k+1}\frac{n-1 \choose n-k}{k} = -1^k \frac{(n-1)!}{(n-k)!k!}=-t_k$$  So, every $t_k$ term is matched with a $t_{n-k}$ terms and they all cancel. Haven't managed to make progress on the case when $n$ is even.    Where did this identity come from? I was studying the  and for the case when all coupons have equal probabilities of being collected, we get the average number of draws until all coupons are collected:  $$E(X) = n \sum_i \frac 1 i$$  If the coupons have different probabilities given by $p_i$ we get:  $$E(X) = \sum_i \frac 1 p_i - \sum_{i<j}\frac 1 {p_i+p_j}+\dots +(-1)^{n+1}\frac{1}{p_1+\dots +p_n}$$  Substituting $p_i=\frac 1 n$ for all $i$ into the second equation and substituting into the first leads to equation (1).


I have a redhat server 7.5. I have a openssh installed on this server. The openssh is 7.4. I need to upgrade openssh 7.4 to 7.6 AS Nessus, vulnerability scanner scanned this vulnerability (Openssh <7.6) and thus need to upgrade to 7.6 or later.The details is found here, .  I found the link,  but they said that this cannot be installed on Red Hat as you cant install bsd on Linux. I referred to this link,   Thus I went to this link,  to have a portable version. I used this link, .  I downloaded this file in /tmp directory.  I performed the following command,  # tar xvfz …/openssh-7.6p1.tar.gz # cd ssh # make obj    ←--------------------  error message # make cleandir # make depend # make # make install   I got this error when I performed the command make obj. The error is  make: *** No rule to make target 'obj'. Stop.


How can I prove that for modular multiplicative inverses that if $∃ $[$b$]$ ∈ℤ_n$ such that [$a$] * [$b$] = [$1$], then gcd($a,n$) =$1$? I understand the relationship between primes and multiplicative inverses, but I am not sure how to prove that if $∃ $[$b$]$ ∈ℤ_n$ such that [$a$] * [$b$] = [$1$], $⇒ $ gcd($a,n$) =$1$ I have some definitions to work with, but I am not sure how to fully write out the proof. gcd($m,n$) is defined as the smallest element of the set $S$ = {$K∈N$ : $k=mx+ny$ for some $x,y∈ℤ$}. I know that gcd($m,n$) = $1$ when they are primes. Multiplicative Inverse for modulo is defined as [$b$]$∈ℤ_n$ if [$a$] * [$b$] = [$1$]. I can prove the converse better, but I am not quite sure how to start with $∃ $[$b$]$ ∈ℤ_n$ such that [$a$] * [$b$] = [$1$] to derive gcd($a,n$) = $1$. I have looked at other posts, but they haven't really shown me what I am looking for. Any help and proofs would be greatly appreciated. Thanks!


Let $(X,d)$ be a metric space and $ A\subseteq X$ be compact. Prove that for any $y \in X$ there exists $x \in A$ so that $d(y,x) = d(y,A)$

Let $ (X,d) $ be a metric space and $ A \subseteq X $ be compact.    Prove that for any $ y \in X $ there exists $ x \in A $ so that $d(y,x) = d(y,A)$ where $ d(x,y)=|x-y| $.   Since A is compact it is covered by finitely many balls of $X$.   So $ A \subseteq \bigcup_{j = 1}^N B(x,j)=B(x,N) .$  Let $y \in A$. Then $y \in B(x,N)$ and so $d(x,y) < N$.  And then I'm stuck on how to approach this problem.


gcd(a,b)=d. Let us have prime numbers k, l so that gcd(ak,bl) = d. Is this valid for all prime numbers?

Let us have two numbers, a, b, so that gcd(a,b)=d. Let us have two prime numbers k,l so that gcd(ak, bl)=d. Is this valid for all prime numbers or is there any conditions that must be met? I guess that it is valid for all prime numbers except those that are divisors of a and b, i.e. kcannot be the prime number which is also divisor of b and lcannot be the prime number which is also divisor of a, but I do not know how to prove it. Could anyone help? Thank you.


How do companies get money from being listed publicly?

How do companies get their money from being on the stock market?  I understand the reason a company will list is to raise capital.  Who gives them this money? The stock market is between buyers and sellers themselves right ? So how do companies get their capital?