Thanks for your help! The plugin finally works. Indeed, p was null, so I changed that and it worked
What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?
Abelian group (Commutative group) Prove that if in a group $(ab)^2= a^2 b^2$ then the group is commutative.  I am having a hard time doing this. Here is what I have so far: Proof:  $a^2 b^2= a^1 a^1 b^1 b^1$ =$aa^{-1}bb$ =ebb Hence,$aa^{-1}=e$  I am stuck, I do not know if this is the right process in proving this Approximating a $\sigma$-algebra by a generating algebra Theorem. Let $(X,\mathcal B,\mu)$ a finite measure space, where $\mu$ is a positive measure. Let $\mathcal A\subset \mathcal B$ an algebra generating $\cal B$. Then for all $B\in\cal B$ and $\varepsilon&gt;0$, we can find $A\in\cal A$ such that $$\mu(A\Delta B)=\mu(A\cup B)-\mu(A\cap B)&lt;\varepsilon.$$  I don't think there is a proof in this site. It's a useful result for several reasons:  We know what the algebra generated by a collection of sets is, but not what the generated $\sigma$-algebra is. The map $\rho\colon \cal B\times\cal B\to \Bbb R_+$, $\rho(A,A')=\mu(A\Delta A')$ gives a pseudo-metric on $\cal B$. This makes a link between generating for an algebra and dense for the pseudo-metric. We say that a $\sigma$-algebra is separable if it's generated by a countable class of sets. In this case, the algebra generated by this class is countable. An with the mentioned result, we can show that $L^p(\mu)$ is separable for $1\leq p&lt;\infty$, which makes a link between the two notions. In ergodic theory, we have to test mixing conditions only an a generating algebra, not on all the $\sigma$-algebra. Is the electromagnetic spectrum discrete? I'm just starting to learn physics and I have a question (that is probably stupid.)  I learned that energy levels that the bound electron can have are discrete. I also learned that when an electron transitions from one level to another, a photon with a specific wavelength (energy) is created and released into the wild.  My question is this: are there holes in the electromagnetic spectrum, values of frequency that the created photon can't possibly have? What exactly is the singleton class in ruby? Can the Help action be used to give advantage to a specific ally's attack (rather than just the next ally who attacks the target)? How do I get back some deleted records? I read through all the related answers, but they do not apply to Ubuntu 14.04.  I have no .gnome2 folder and no Passwords and Encryption keys item in the system settings. I tried to crawl through every possible menu, but I could not find out how to do it.  The popup usually pops out when I start Chromium. This question led to a new package:      I wish to typeset some relatively long URLs in a piece of text, and when I use \url{..}, the resulting text does not respect the margin boundaries that govern the main text body, instead going all the way to the edge of the paper before wrapping around.   For reference, my preamble looks like this:  \documentclass[12pt]{article} \usepackage{mathptmx} \usepackage{fullpage} \usepackage[pdftex]{hyperref}   and example of the url I'm including is:  \begin{itemize} \item Some text  \url{very-long-url} ... \end{itemize}   I'm compiling using pdflatex, although I doubt this makes a difference. I want to create a DEB file manually. I would like to just provide a folder which contains data to install, and a script to be executed after installation.  Is this possible? What can I use to typeset MATLAB code in my document? This question led to a new package:      Does anybody have a quick and easy way to typeset some relatively long MATLAB code in the appendix? I looked up a few methods, and the mcode package emerged as a possibility, but it seems to be unmaintained...  I have a ton of equations in my code, so I'd prefer a solution that avoids having to use $ to denote equations.  Also, if possible, if there's a way to keep all of MATLAB's "natural" coding colors (e.g. green for comments), that would be great...  Any idea? I sometimes get files from my clients that have the wrong file extension. For example, the name is image.jpg but the file is actually a TIFF image. In many cases I can clarify it by opening the file in a text editor, looking at the first few bytes, then deducing which file type it is.  This works for me with JPEG, TIFF, GIF and PDF files. However there are many more file types out there.  Is it possible to automate identification of the correct file type by analyzing the containing data? Is there are rule when to use opened vs open?  I always get confused even though I've been speaking English as the dominant language for more than half my life.  E.g.         Is the door open(ed)?   Which file do you have open(ed) in your editor? My linear voltage regulator is overheating very fast I'm using a 5 V / 2 A voltage regulator () without a heatsink. I'm testing the circuit with a microcontroller (PIC18FXXXX), a few LEDs and a 1 mA piezzo buzzer. The input voltage is aprox. 24 VDC. After running for a minute, the voltage regulator starts to overheat, meaning it burns my finger if I keep it there for more than a second. Within a few minutes it starts to smell like it's burnt. Is this a normal behavior for this regulator? What could cause it to heat that much?    Other components used in this circuit:  L1:   R2:   F1: Italian keyboard: entering tilde (~) and backtick (`) characters without changing keyboard layout highest power of prime $p$ dividing $\binom{m+n}{n}$ How do I summon a baby mob? In Minecraft Java Edition, one can summon baby zombies and drowned using the IsBaby NBT tag: /summon zombie X Y Z {IsBaby:1b}  Likewise, one can summon baby breedable mobs (Pigs, Cows, etc.) by giving them a negative Age NBT tag (the number of ticks until the mob grows up): /summon cow X Y Z {Age:-100000}  Since NBT is inaccessible from commands in Bedrock Edition, the above commands will not work there. How do I summon baby mobs in Minecraft Bedrock Edition? Compile error with \href ToC and \apacite I would like to edit my document but I have a compile error somewhere between the \href and the apacite but can't locate it. I've tried blocking out code and taking out references, with varying results.  \documentclass[a4paper,12pt]{article} \usepackage[english]{babel} \usepackage[utf8]{inputenc}  % TOC, Citations, Refereneces, and Appendicies \usepackage{apacite} % \cite{ref1,ref2} %Warning - unsupported tocstyle code \usepackage[tocindentauto]{tocstyle}     \renewcommand{\thesection}{\Roman{section}}      \renewcommand{\thesubsection}{\arabic{subsection}.}     \renewcommand{\thesubsubsection}{\roman{subsubsection}.} %\usepackage{hyperref} %\urlstyle{same} %\hypersetup{ %   colorlinks=true, %   urlcolor=cyan, %   linkcolor=blue, %   citecolor=green, %   filecolor=magenta, %   pdftitle={Sharelatex Example}, %   pdfpagemode=FullScreen, %} \usepackage[toc,page]{appendix}  \begin{document}    ...to be installed \cite{church13,hershkowits97}. \bibliographystyle{apacite} \bibliography{bibliography} \end{document}   Here are the bibliography.bib entries then  @ARTICLE{church13,    author       = {K.H. Church and H. Tsang and R. Rodrigiguez and P. Defembaugh and R. Rumpf},    year         = 2013,    title        = {Printed circuit structures, the evolution of printed circuit boards},    journal      = {Circuit Insight},    volume       = {},    number       = {},    pages        = {},    howpublished = {},     url          = {http://www.808multimedia.com/winnt/kernel.htm}, }  @ARTICLE{hershkowits97,    author       = {N. Hershkowits and R.A. Breun},    year         = {1997},    title        = {Diagnostics for plasma processing (etch plasmas) (invited)},    journal      = {Review of Scientific Instrumentation},    volume       = {68},    number       = {1},    pages        = {880--885},    howpublished = {}, } I'm teaching my self topology with the aid of a book. I'm trying to prove the following is a topology:     Let X be an infinite set. Show that $\mathscr{T}_2=\{U \subseteq X : U = \emptyset $ or $ X\setminus U $ is countable$ \} $ is a topology.   My book calls this set the ""  Please let me know if my proof is valid.     corollary [A]: The union of countable sets are countable.    proof: I'm going to take as a given that that the union of finite set are finite, and just prove the case of . A set is countable infinite if there is a bijection between the set and the natural numbers. Let $A$ and $B$ be a countable infinite sets. Now let $f$ be the bijection between $A$ and $\mathbb{N}$ and $g$ be $B$'s bijection.  $f:\mathbb{N}  \rightarrow  A$  $g:  \mathbb{N}  \rightarrow B$  There can always exist a bijection $h$ that maps $A \cup B $ to $\mathbb{N}$. To account for non disjoint sets, let $B' = B \setminus A$; (note: $A \cup B = A \cup B'$)  $h:  \mathbb{N}   \rightarrow  A \cup B'$  $ h(x) = \left\{         \begin{array}{ll}             f(\frac{1}{2}x); &amp; \quad x \in 2\mathbb{N} \\             g(\frac{x+1}{2}); &amp; \quad x \in 2\mathbb{N}+1         \end{array}     \right. $   $h^{-1}(x)$ would map $A$ to the even numbers, and $B'$ to the odd numbers.  Therefore, The union of countable sets are countable. (QED)  Now to verify the definition.     (i) X and Ø are elements of $\mathscr{T}$.   Ø is given in the definition of $\mathscr{T}_2$. Also, the empty set is considered finite, with cardinality zero. Thus $X$ is in $\mathscr{T}_1$ because its complement is finite, and finite numbers are countable.      (ii) $\mathscr{T}$ is closed under finite intersections.   Let:$V_k \subseteq X$ be any countable set. (ie: $V_1, V_2...$ are all countable sets)  So Then, $U_k = X \setminus V_k$, would be the subsets of $\mathscr{T}_2$.  $U_k \cap U_j = X \setminus (V_k \cup V_j) $, due to De Morgan's law.   Thus, $U_k \cap U_j \in  \mathscr{T}_2$, since the Union of two countable sets is also countable[A]. And This reasoning can be extended to any finite amount of intersections.       (iii) $\mathscr{T}$ is closed under arbitrary unions.   Let $A=\bigcup_{i \in I} U_i$ be an arbitrary union of sets whose complements are are countable.Then by De Morgan's law, $A=X \setminus (\bigcap_{i \in I}V_i)$, for some countable sets $V_i$. By the definition of intersection, $\bigcap_{i \in I}V_i \subseteq V_i$ for all $i \in I$. Since $V_i$ is countable so is any of its subsets.  Hence the complement of $A$ is countable. How can I concatenate regex literals in JavaScript? Is it possible to do something like this?  var pattern = /some regex segment/ + /* comment here */     /another segment/;   Or do I have to use new RegExp() syntax and concatenate a string? I'd prefer to use the literal as the code is both more self-evident and concise. Find two elements that don't have a gcd in a subring of Gaussian integers