How do a black hole made from electrons produce EM field?
Detection of the Electric Charge of a Black Hole
What is the best way to return an error from a function when I'm already returning a value? What is the best practice for multiple button placement and emphasis? Usually, we only have 2 buttons at the bottom of a form or a page that requires an action: Submit &amp; Cancel.  This one is quite easy to style. However, what if we are dealing with multiple buttons at the bottom of a page? For example:   ← Back | Send Email | Booking Paid | Check-in Guest   I'm thinking of making "Back" just a link (not a button) and making "Send Email" / "Booking Paid" secondary buttons (light gray). Then I'd make "Check-in Guest" as the primary button (green).  I still feel that there's a better way of doing it or dealing with multiple buttons / actions. What do you think? What's the difference between  and ,  and ? What's the difference between &lt;b&gt; and &lt;strong&gt;, &lt;i&gt; and &lt;em&gt; in HTML/XHTML? When should you use each? What to do if a referee plagiarises the result after rejecting a paper? What is wrong with this chi-squared calculation? I am calculating chi-squared in R and manually, and getting two different answers. I believe that R is correct, but I am not 100% sure.  Can someone please help me understand why?  In R:  test           &lt;- matrix(c(4203, 4218, 786, 771), ncol=2) dimnames(test) &lt;- list(group = c("control","exp"), click = c("n","y")) print(test) print(Xsq      &lt;- chisq.test(test, correct=F))    This gives me $\chi^2 = 0.1712$.  If I do this by hand, however, I get $0.339$.  Here is my calculation: \begin{align} \frac{(E1 - O1)^2}{E1}     &amp;+ \frac{(E2 - O2)^2}{E2}    &amp;  \\ \frac{(4203-4218)^2}{4203} &amp;+ \frac{(771 - 786)^2}{786} &amp;= .3398 \end{align} Why did the Star Trek writers decide Warp 10 would be infinite? From  onward,  has a basically cubic scale from warps 1 - 9. But then, close to warp 10, it suddenly develops its own puzzling scale, as can be seen in .  In this scale, , occupying all points in the universe simultaneously and therefore effectively teleporting instantaneously.  My question is why have this confusing scale? Why not have a uniform cubic scale? Was there ever any "official" explanation for this?  Clarification: I'm looking for why the writers decided on this, not the "in-universe" explanation. Seeing that Defense Against the Dark Arts is a crucial subject, both in Harry's life as well as a part of the school-going wizard's curriculum, it must be in the hands of a good professor.   Is it known who Minerva McGonagall appointed as DADA prof. once she was made Headmistress. Was it someone we know or was it just a random powerful wizard. Is there any information about this available? Bash File Unable to locate package when new line is added When building a bash file to execute I keep getting an error after adding a new line. I have tried moving some lines around or removing some of the packages but it will results in the same error. In the file if I was to remove 3 and 4 it there will no longer be an error.   E: Unable to locate package &lt;package&gt;   The bash file looks like this   #!/usr/bin/env bash sudo apt update &amp;&amp; sudo apt install -y python3-pip build-essential python3-dev python3-setuptools gcc sshpass sudo apt-get install apt-transport-https lsb-release software-properties-common dirmngr sudo apt-get update   The output with the error  Hit:1 http://us.archive.ubuntu.com/ubuntu bionic InRelease Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]                                                   Hit:3 http://archive.ubuntu.com/ubuntu bionic InRelease                                             Get:4 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]         Get:5 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]                                       Fetched 252 kB in 1s (189 kB/s)     Reading package lists... Done Building dependency tree        Reading state information... Done All packages are up to date. Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package sshpass Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package dirmngr Hit:1 http://us.archive.ubuntu.com/ubuntu bionic InRelease Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]                                                   Hit:3 http://archive.ubuntu.com/ubuntu bionic InRelease                                             Get:4 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]         Get:5 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]                                       Fetched 252 kB in 1s (209 kB/s)     Reading package lists... Done Modelling population with $\frac{dP}{dt}=P(\beta - \delta P)$ What's the best way to store class variables in PHP? I currently have my PHP class variables set up like this:  class someThing {      private $cat;     private $dog;     private $mouse;     private $hamster;     private $zebra;     private $lion;      //getters, setters and other methods }   But I've also seen people using a single array to store all the variables:  class someThing {      private $data = array();      //getters, setters and other methods }   Which do you use, and why? What are the advantages and disadvantages of each? Why should the interface for a Java class be preferred? would report a violation for:  ArrayList&lt;Object&gt; list = new ArrayList&lt;Object&gt;();   The violation was "Avoid using implementation types like 'ArrayList'; use the interface instead".  The following line would correct the violation:  List&lt;Object&gt; list = new ArrayList&lt;Object&gt;();   Why should the latter with List be used instead of ArrayList? nvidia-libopencl1-331 has to be removed before installing WINE I don't know much about this,  But I've some of the questions on which some user has answered (not helpful answer) also but I want to delete those questions, but whenever I go to delete that question. It is prompting with     What does it mean? Can someone tell me what would be the action taken by Stack Exchange if I delete more questions? Kernel of composition of linear transformations Let $f : U \to V$ and $g : V \to W$ be linear transformations on the vector spaces $U$, $V$, and $W$. Supposedly,  $$ \dim(\ker(g \circ f)) = \dim(\ker(f)) + \dim(\ker(g) \cap \operatorname{im}(f)). $$  How might I go about proving that?    (Attempt:) The $\dim(\ker(g)\cap\operatorname{im}(f))$ term suggests to me that I should define a vector space $V' = \ker(g) + \operatorname{im}(f)$ to invoke the theorem that  $$ \dim(V') = \dim(\ker(g)) + \dim(\operatorname{im}(f)) - \dim(\ker(g) \cap \operatorname{im}(f)), $$  but I don't really see where to go from there. It seems that OTP encryption is unbreakable. I have read some articles (Wikipedia, Blogpost, etc.), but I could not find any information about how they are used.  If I wanted to create a messenger service, how would I distribute the OTP keys? Both the sender and the receiver need this key before the message is sent, right?   And how do I make sure no one else gets these keys? Zip using Oracle Stored Procedure When I right click the Filezilla icon, the only options are "launch" and "properties". How do I remove it from the top panel? Redirect console output to textbox in separate program I'm developing an Windows Forms application that requires me to call a separate program to perform a task.  The program is a console application and I need to redirect standard output from the console to a TextBox in my program.    I have no problem executing the program from my application, but I don't know how to redirect the output to my application.  I need to capture output while the program is running using events.    The console program isn't meant to stop running until my application stops and the text changes constantly at random intervals.  What I'm attempting to do is simply hook output from the console to trigger an event handler which can then be used to update the TextBox.  I am using C# to code the program and using the .NET framework for development.  The original application is not a .NET program.  EDIT: Here's example code of what I'm trying to do.  In my final app, I'll replace Console.WriteLine with code to update the TextBox.  I tried to set a breakpoint in my event handler, and it isn't even reached.      void Method()     {         var p = new Process();         var path = @"C:\ConsoleApp.exe";          p.StartInfo.FileName = path;         p.StartInfo.UseShellExecute = false;         p.OutputDataReceived += p_OutputDataReceived;          p.Start();     }      static void p_OutputDataReceived(object sender, DataReceivedEventArgs e)     {         Console.WriteLine("&gt;&gt;&gt; {0}", e.Data);     } How can I get id,class or name attr an element with jquery What is object slicing? Someone mentioned it in the IRC as the slicing problem.