what does !function in Javascript mean?
What does the exclamation mark do before the function?
I am trying to find all the Sylow 2 subgroups of S4 using Sylow’s theorems. Now, I know that a Sylow 2 subgroup of S4 has size 8, and that there are either 1 or 3 of them (as the number of of Sylow 2-subgroups has form 1+2k and divides 3, the index).  Now my lecturer states “stabilisers of the 3 different bisections of {1,2,3,4} yield 3 distinct Sylow 2 subgroups”  Now my questions are:  1) What does it mean by stabilisers of 3 different bijections of {1,2,3,4}? Is that to say the elements of S4 which send {1,2} and {3,4} to {1,2},{3,4} i.e. by (12)(34)?  2) How does he know that there are 8 elements of this set? Perhaps this will become clearer after the 1st question is answered.  Many thanks, group theory is hard. I've updated my Ubuntu to 19.10 couple of weeks ago and on installation system suggests to change or add shortcut for input source selection despite one was already defined previously. I've added ctrl+shift shortcut and just realized that it somehow overlapped any other ctrl+shift+something shortcuts globally, i.e. when I want to open new window in vscode, it opens new tab and it looks like system doesn't see the shift button press.   I tried to search this combination in shortcuts settings, but it's just not there. Handle .bib in subfiles I have a problem very similar to the question being asked in  . My .bib is references in main.tex. When compiling main, everything works like a charm. Working on the subfiles, I have two issues though (which are most likely related):   I can't access the bib with auto-completion When compiling the subfile, it doesn't insert the citations.   I tried including  \bibliographystyle{plainnat} \bibliography{mybib}   in the subfiles, which also worked smoothly. Obviously, the bibs are included in every chapter of the document when compiling main.tex, then. I tried setting a global boolean in main.tex:  \newboolean{printBibInSubfiles} \setboolean{printBibInSubfiles}{false}    and in the subfiles:  \ifthenelse{\boolean{printBibInSubfiles}}    {}    {\bibliographystyle{plainnat}     \bibliography{../betterbib.bib}}    For some reason, then setting the boolean to false, the "bibliography"-header was printed in the subfiles as well as for the main file, but there was no output of citations under any of the "bibliography"-headers. Furthermore, compiling only the subfiles didn't work correctly.  My document structure is the following:  main.tex:  \begin[document] ... \subfile{sub/dataprocessing} ... \bibliographystyle{plainnat} \bibliography{mybib} \end{document}   the subfiles:  \documentclass[../main.tex]{subfiles} \begin{document} ... \cite{Random2014} ... \end{document}   After all this explanation: the only thing I want is to access the .bib from the subfiles without having to manually uncommenting something when compiling the main file. Any takers?  PS: Obviously, I also tried the solution provided in "" but couldn't get it to work. I don't know whether that would solve my problem anyway, since I don't have the \printbibliography-issue of the thread opener. 32 bit or 64 bit OS on a 512 mb VPS? I am planning to rent a VPS service with following basic specification:   512mb of RAM 1 CPU 20gb HDD (4gb of it is swap) Ubuntu 10.10 server   I am able to choose between a 32 bit or 64 bit install of Ubuntu server as the operating system.   My question is would it be better to chose a 32 bit operating system since I will have only 512mb of RAM, rather than using a 64 bit operating system and dealing with the additional overheads?  edit:  I have installed Ubuntu server 10.10 32 bit and 64 bit on VirtualBox. After a minimalistic installation with only ssh server, the 32 bit installation consumes 63mb of RAM when first boot up and 64 bit consumes 85mb of RAM.  After installing and running  daemon, 32 bit consumes 99mb of RAM when first boot up and 64 bit consumes 128mb. Cauchy Problem for inviscid Burgers' equation Consider the Cauchy Problem of finding $u(x,t)$ such that    $$\frac{\partial u}{\partial t}+u\frac{\partial u}{\partial x}=0,x\in\mathbb{R},t&gt;0$$ $$u(x,0) = u_0(x), x\in\mathbb{R}$$ Which choices of the following functions for   $u_{0}$ yield a $C^{1}$ solution $u(x,t)$ for all   $x\in\mathbb{R},t&gt;0$         $u_{0}(x)=\frac{1}{1+x^{2}}$   $u_{0}(x)=x$   $u_{0}(x)=1+x^{2}$   $u_{0}(x)=1+2x$.      If I use the existence and uniqueness theorem for Cauchy problem i get the corresponding determinant is non zero so all are true according to me. But in answer key only option 2nd and 4th is given. Please help me to solve the problem. Thanks a lot. It would help everyone if we provided a mechanism that people could use to flag their post if English is language they are not comfortably fluent in. A lot of non-English speakers have to go to English forums for tech support and find it embarrassing to ask questions in broken Englis.   Worse, people reading a post often cannot tell if a badly-worded post results from a poor English or just laziness and sloppiness on the part of a native English speaker. Personally, I will take the time to puzzle out a poorly-worded post if I know the author is struggling with English, but if I think they're just lazy and careless I won't bother.   A simple check box could flag the author as a non-English speaker and allow everyone to adjust accordingly.   Edit01:  Some answers below have accused me of being 'elitist'. I'm not sure where they got the idea that I was sneering down at anyone because their abilities at either English or coding. That was not my intent.   When I said I would not bother with post that appeared to incoherent owing to laziness or carelessness, I am not being elitist. I'm giving priority in my time budget to people who are respectful enough of my time to spend the their time writing as clear a question as their grasp of English and coding allows. Why should I spend time answering a careless and slapdash post when I could spend that time helping posters who took more of their time writing their questions?   I am perfectly willing to burn a lot of time helping someone struggling to write code in their non-native language. I have a hard enough time coding myself in English that I can't even imagine what a dog's breakfast I would make of it if I had to code in, say, Korean.    I have seen many instances in which questions have been downvoted when a quick glance at the poster's profile gives a strong hint they are not native English speakers. I would like a system that would spare those posters from being downvoted or ignored by using an interface element that clearly communicates in a standardized way whether the poster natively speaks English or not.   I don't see what's elitist about that.    Edit02:   (original unedited) I'm talking about:     Hy, I have a childe view that put it   self over other brother views. The   problem is that when i touch it the   brother also reacts at the touch   event. How can I disable touch   propagation on the underlieng brother   views?   I'm not even exactly sure what he is describing. I can guess that he has a sibling view that extends over its siblings but I'm not sure. If I edited it, I might not end up asking the same question the poster intended.   To answer the question, I will either have to (1) first ask for more detail and then keep checking back until I get it or (2) try to answer what I think the question is and possibly mangle it then have to come back and edit my answer all the while risking a downvote because I answered the wrong question.   I will take the time and the risk of down vote if the poster is not a native English speaker (or is a child) and the confusing question represents their honest best effort. If they're just being lazy, I have other people to help.   I would like a mechanism that would help me decide how to allocate my time and would protect the non-English speaking posters from unjust downvotes. Can't Use /Summon Command Recently I've been messing around with making a few minigames, and have used a few plugins to help make it easier to create and run them. However, a newer one I'm making requires me to use the /summon command in order to spawn zombies. However, no matter what I put in, I can't spawn hostile mobs. All other entities still spawn perfectly fine. Strangely, the /spawnmob command which comes with Essentials can summon hostile mobs fine. I would rather use /summon since it's more customizable though. Here's a list of plugins I have installed.   Essentials EssentialsChat HolographicDisplays PermissionsEx setspawn [A plugin I have made, just a simple timer] Vault VoxelSniper WorldEdit WorldGuard   Please let me know if you have any ideas on what I'm doing incorrectly or isn't functioning the way it should. Are more megapixels good?  Are more megapixels bad?  Do more megapixels increase detail? Do they make my images sharper? On the other side, is there a point that is too much? Do megapixels cause increased noise and other problems? How does print and viewing size come into it?  Widespread Internet-forum wisdom used to be that 6 megapixels was the sweet spot — below that just wasn't enough, but above that, there wasn't much benefit. File sizes got larger, but detail was lost to noise and other problems. The arguments are that cramming too many pixels into a small sensor makes each pixel too small to provide any real benefit, and that higher-megapixel sensors outresolve cheap lenses anyway. (Substitute something like 12 instead of 6 if we're discussing APS-C DSLRs, or 24 for full-frame.)  By 2011,  was in the range of 12-18 megapixels. In 2016 most were are in the 16-24 megapixel range. Certainly none are at 6 anymore; even smartphones come with 8 megapixel cameras. Does this offer any real improvement over that old "sweet spot"? Has technology improved to the point where the "wisdom" needs to be updated, or are we all suffering for marketing? Or have we gone past the sweet spot in some ways, but it's okay because of previously-un-argued points. (For example: more noise, sure, but more detail as well.)  Within the 16-24 megapixel common-today range, for the same sensor size, is there any actual benefit to the higher end? How do megapixels directly affect image quality with today's technology? What are the benefits and when do they apply? What are the drawbacks, and when do they apply? How should I adjust my technique (and expectations) based on my camera's megapixel count? What are all of the connected subsets of $\mathbb{Q}$? The answer are the singletons of $\mathbb{Q}$. I can show that the open intervals of $\mathbb{Q}$ are disconnected by choosing some irrational in the open set and using it to form a separation. But strangely enough, I am having a hard time seeing why the subset $\{p,q \}$ of $\mathbb{Q}$ is disconnected. If say $p &lt; q$ and we choose some irrational $p &lt; x &lt;q$, the separation of $\{p,q \}$ would, I think, be given by $ \{p\}$ and $\{q\}$. But these aren't open in $\mathbb{Q}$ ...? Let $a$, $b$, and $c$ be integers, where a $\ne$ 0. Then $$ $$ (i) if $a$ | $b$ and $a$ | $c$, then $a$ | ($b+c$) $$ $$ (ii) if $a$ | $b$ then $a$|$bc$ for all integers $c$; $$ $$ (iii) if $a$ |$b$ and $b$|$c$, then $a$|$c$.  Prove that if $a$|$b$ and $b$|$c$ then $a$|$c$ using a column proof that has steps in the first column and the reason for the step in the second column.  My book is really vague. I'm not really sure what to do..  First I was thinking something like this: $a\mid b\Rightarrow b=as$ and  $b\mid c\Rightarrow c=bt$ and $a\mid c\Rightarrow c = au$ $$ $$ $b + c + c = b + 2c$  $$ $$ $=as + 2(bt+au)$  Yea then I just got lost. Are repository updates secure?  As a bear of little brain from the developer side, I cannot understand why the repository list is http://security.ubuntu.com and the other http(unsecured) sites listed in /etc/apt/sources.list.  Without a certificate chain match this appears as "ask any responder for a list of packages to update" instead of "ask the ubuntu.com site..."  Can any network choose to spoof the update sites, and is this a common practice to provide a locally cached and vetted copy? E: Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable) I'm trying to run this command in the terminal:  sudo apt install software-properties-common   This is the error message I get:  E: Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable)   E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend),     is another process using it? What is the purpose of LongLength for .Net Arrays? Use a LookUp field in a Calculated Column Can I make a script always execute as root? What does $$ mean in the shell? How do you match only valid roman numerals with a regular expression? Thinking about , i decided I can't even create a regular expression that will match roman numerals (let alone a context-free grammar that will generate them)  The problem is matching only valid roman numerals.  Eg, 990 is NOT "XM", it's "CMXC"  My problem in making the regex for this is that in order to allow or not allow certain characters, I need to look back. Let's take thousands and hundreds, for example.  I can allow M{0,2}C?M (to allow for 900, 1000, 1900, 2000, 2900 and 3000). However, If the match is on CM, I can't allow following characters to be C or D (because I'm already at 900).  How can I express this in a regex? If it's simply not expressible in a regex, is it expressible in a context-free grammar? Please add Right To Left text support in Stack Exchange You know, some of us read right to left...  Certain sites like  and  have an obvious need for this, as Arabic and Hebrew are Right To Left (RTL) languages. Many answers on those sites cite the Torah and the Quran respectively. Directly quoting these sources properly requires RTL text. So, I'm running linux Mint (but I guess the same applies to Ubuntu) and as is common knowledge, their TeX distribution tends to be slightly outdated. Now I can't have none of that and decide to install it with the install-tl from the TeXlive homepage. Somehow, I cannot install it as a normal user (this I find normal as it is installing in the root directory), so I proceed to install TeXlive   sudo perl ./install-tl   and add the paths to .bashrc. All is well and my TeXlive installation works. Except for the texhash option. Running it as a normal user is no problem, except that I installed TeXlive as root, and so running texhash as normal user doesn't do anything (directory not writable. Skipping...). No problem I think, I'll just do it as root. But somehow texhash isn't installed for root.  Now, texhash is somehow connected to updating the directory tree, but I don't really know what it does. I use it on my ~/texmf/ folder to add my packages to a global path (I think), but when looking at info for this question I see in a comment for  question that this is apparently not needed, though I don't understand what I'm to do now.  So if I'm not adding new packages from CTAN or updating, I really don't need texhash and all is good?   To summarize: I'd like to know:    Why should I need texhash? Can I avoid installing as root on linux Mint/ubuntu ( they say you don't have to be root, that it's even discouraged)? Should I somehow install texhash for root?   I realize this might be a vague question at best, but I didn't find an answer I readily understood, so I'd appreciate any thought on this. What is LookDev/Material Preview mode for in 2.8?