$x ≡ a \pmod{m}, x ≡ b\pmod{n}, x ≡ c\pmod{r}$
Give an example of three positive integers m, n, and r
Suppose the default shell for my account is zsh but I opened the terminal and fired up bash and executed a script named prac002.sh, which shell interpreter would be used to execute the script, zsh or bash? Consider the following example:  papagolf@Sierra ~/My Files/My Programs/Learning/Shell % sudo cat /etc/passwd | grep papagolf [sudo] password for papagolf:  papagolf:x:1000:1001:Rex,,,:/home/papagolf:/usr/bin/zsh # papagolf's default shell is zsh  papagolf@Sierra ~/My Files/My Programs/Learning/Shell % bash # I fired up bash. (See that '%' prompt in zsh changes to '$' prompt, indicating bash.)  papagolf@Sierra:~/My Files/My Programs/Learning/Shell$ ./prac002.sh  Enter username : Rex Rex # Which interpreter did it just use?   **EDIT : ** Here's the content of the script  papagolf@Sierra ~/My Files/My Programs/Learning/Shell % cat ./prac002.sh  read -p "Enter username : " uname echo $uname Comprehensive book on group theory for physicists? I am looking for a good source on group theory aimed at physicists. I'd prefer one with a good general introduction to group theory, not just focusing on Lie groups or crystal groups but one that covers "all" the basics, and then, in addition, talks about the specific subjects of group theory relevant to physicists, i.e. also some stuff on representations etc.  Is Wigner's text a good way to start? I guess it's a "classic", but I fear that its notation might be a bit outdated? Images are escaping from the help center privilege page Images included in the fully expanded privilege pages are escaping from the body.    This is most noticeable on the  (which I know is going away soon anyway):    But is also apparent on:       In the edit page preview, the images sit correctly within the borders.  Chrome 27, Windows 7 External Hard Drive no longer working I am on a MacBook Pro 13 running latest Sierra. I have an external Seagate solid state hard drive that was working and out of the blue stopped working. The only thing on it was my Adobe Lightroom images/videos. Not the LR DB files. I'm sure you have all heard this woe before, so I won't dwell on that. And yes, I back up to the cloud. AWS S3 specifically. Though I am traveling South East Asia for the last year, and staying in cheap hostels. So good internet is hard to come by sometimes. I can't back it up after every export. While most of it is backed up, there is some that is not.  Moving on. The symptoms seems to change every time I plug it in. The first sign was it ejected on it's own. I plugged it in again, and it wouldn't mount. Disk Utility recognized it, so did the command line diskutil list but it wouldn't mount. I rebooted and it worked for a second. Then I could only get to it from the command line. Then trying to frantically back up to my local what was not backed up to the cloud, it all failed. Basically just a cp -R [directory] [local-directory] command.  After some more frantic unplugging and re-plugging plus some command line manual mounts, I finally got it to where the Disk Utility would be able to run first aid on it. It failed. I don't recall the error. So I put it in a freezer. After a few hours I tried again. It is not any better. It still will not mount. Now Disk Utility sees it, but with no partition. I can't even give me information about how much space is used on it.  I have also tried it from a Windows machine. It did not mount. I have tried other cables. No success. As well as tried my other USB port. I also have another working external hard drive exactly like the one giving me issues. It works on all cables and USB ports.  I do have Docker running with a Ubuntu container, I'm trying to think of a way to see if I can try to get to the USB from there. I also have a USB that I have thought about running a live Ubuntu on there to see if I can mount and retrieve the data or fix the HDD that way. But if it will not mount, I doubt these will work.  Can anyone else think of any other tricks I can try myself to see if I can repair this or at least retrieve the data without paying for a service or software? If not, those suggestions are also welcome.  Update   I made the mistake in original post that it was a Solid State Drive. This is my mistake, it is actually a spinning disk hard drive. I bought them long ago and have been traveling with them for so long I just forgot. Question is updated to reflect this. Now diskutil list does not show it at all. The Disk Utility app also does not see it. Based on suggestion from @Allen I seeked out the USB to SATA cable. I did not quite find it, as my options are extremely limited where I am at. Though a local expat on a facebook group was able to help me with a empty 2.5 casing that I was able to extract the drive from original casing and put it in his blank case. It now mounts. Though it has the "click of death" sound to it. And data is not really reachable. While I can ls the directories and Adobe Lightroom does not have the exclamation mark when it can not reach the actual external files. Right clicking on the images and clicking on "Show in Finder" or any other variation of trying to get to the files through Finder or terminal, I have no success. It usually hangs and I get the spinning wheel. Since Adobe Lightroom imports these images into directories named by date, I am going to send the drive off to a data recovery service and ask to recover just unbacked up directories i.e. dates. Next time I will make harder efforts to backup and probably get an actual SSD.   I think this can be closed, due to my low reputation points I can not close this myself. Is it possible to check a bash script syntax without executing it?  Using Perl, I can run perl -c 'script name'. Is there any equivalent command for bash scripts? Resizing an iframe based on content I am working on an iGoogle-like application. Content from other applications (on other domains) is shown using iframes.   How do I resize the iframes to fit the height of the iframes' content?  I've tried to decipher the javascript Google uses but it's obfuscated, and searching the web has been fruitless so far.  Update: Please note that content is loaded from other domains, so the  applies. $\sin \frac{1}{x}$ is not uniformly continuous on $[1, \infty]$ Postfix Connection Timed out Variance of Wilcoxon Rank-Sum Test (no ties) $\newcommand{\E}[1]{\mathbb{E}\left[#1\right]} \newcommand{\r}[1]{r\left(#1\right)} \newcommand{\P}[1]{\mathbb{P}\left(#1\right)} \newcommand{\Var}[1]{\text{Var}\left[#1\right]}$  Given two sets of data $X$ with $m$ points and $Y$ with $n$ points, unioned (keeping duplicates) to create a data set $Z = \{Z_i\}$ with $m + n = N$ data points, the Wilcoxon Rank-Sum Test Statistic is given by \begin{equation*} T = \sum\limits_{i=1}^{N}r(Z_i)\cdot \mathbb{I}(Z_i \in X)\text{,} \end{equation*} where $\mathbb{I}(Z_i \in X)$ is $1$ if $Z_i \in X$, $0$ otherwise. ($r(\cdot)$ denotes the rank of the data point.)  Suppose there are no ties. Then  \begin{align*} \E{T} = \sum\limits_{i=1}^{N}\r{Z_i}\cdot \E{\mathbb{I}(Z_i \in X)} &amp;= \sum\limits_{i=1}^{N}\r{Z_i}\cdot\P{Z_i \in X} \\ &amp;= \dfrac{m}{N}\sum\limits_{i=1}^{N}\r{Z_i} \\ &amp;= \dfrac{mN(N+1)}{2N} \\ &amp;= \dfrac{m(N+1)}{2}\text{.} \end{align*} This comes out to what it says in the book Nonparametric Statistical Inference, 5th ed., by Gibbons and Chakraborti.  Now for $\Var{T}$: \begin{align*} \Var{T} &amp;= \Var{\sum\limits_{i=1}^{N}\r{Z_i}\mathbb{I}(Z_i \in X)}\\ &amp;= \sum\limits_{i=1}^{N}\left[\r{Z_i}\right]^2\Var{\mathbb{I}(Z_i \in X)} \\ &amp;= \sum\limits_{i=1}^{N}\left[\r{Z_i}\right]^2\P{Z_i \in X}\left[1-\P{Z_i \in X}\right]\\ &amp;= \left(\dfrac{m}{N}\right)\left(1-\dfrac{m}{N}\right)\sum\limits_{i=1}^{N}\left[\r{Z_i}\right]^2 \\ &amp;= \left(\dfrac{m}{N}\right)\left(1-\dfrac{m}{N}\right)\left[\dfrac{N(N+1)(2N+1)}{6}\right] \\ &amp;= \left(\dfrac{m}{N}\right)\left(\dfrac{N-m}{N}\right)\left[\dfrac{N(N+1)(2N+1)}{6}\right] \\ &amp;= \left(\dfrac{m}{N}\right)\left(\dfrac{n}{N}\right)\left[\dfrac{N(N+1)(2N+1)}{6}\right] \\ &amp;= \dfrac{2N+1}{N}\left[\dfrac{mn(N+1)}{6}\right] \end{align*} The answer should be $\dfrac{mn(N+1)}{12}$. What did I do wrong? Submodule of free module over a p.i.d. is free even when the module is not finitely generated? How to convert from one grading scheme to another? Problems updating Python from the repositories today (Feb 25, 2021) NOTE: This is a Master Canonical Post for the issues observed on February 25, 2020.  All issues on Feb 25 relating to Python updates not found should be dupe-linked here.  Errors have been seen such as this today, February 25, 2021: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/p/python2.7/libpython2.7-minimal_2.7.17-1~18.04ubuntu1.3_amd64.deb 404 Not Found  Is there something up with the repositories? Why does resistivity increase with temperature?  The explanations I have heard so far are that increasing temperature increases vibrations in the lattice structure resulting in the number of collisions increasing.  But the vibrations from thermal energy are random, so around half of the vibrations would result in the atoms moving out of the electrons way and half would result in atoms moving into the way of the electrons.  And since half of the vibrations result in increasing the drift speed and half reduce it, shouldn't the average drift speed remain the same? Understanding etoolbox \ifdefempty and \ifdefvoid I am trying to understand the  \ifdefempty and \ifdefvoid macros. The documentation says that \ifdefempty     Expands to true if the control sequence is defined and is a   parameterless macro whose replacement text is empty, and to false   otherwise.   Similarly \ifdefvoid     Expands to true if the control sequence is undefined, if is a macro   whose meaning is \relax, or a parameterless macro whose replacement   text is empty, and to false otherwise.   From these descriptions I thought that \def\myempty{}, \def\myrelax{\relax}, and \def\myemptyempty{\myempty} would all be both "empty" and "void", but \def\myempty{} is the only one that is either "empty" or "void". What am I missing?  \documentclass{minimal} \usepackage{etoolbox}  \begin{document}  \def\myempty{} \def\myrelax{\relax} \def\myemptyempty{\myempty}   \ifdefempty{\myempty}{Empty}{Not empty}  \ifdefempty{\myrelax}{Empty}{Not empty}  \ifdefempty{\myemptyempty}{Empty}{Not empty}  \ifdefvoid{\myempty}{Void}{Not void}  \ifdefvoid{\myrelax}{Void}{Not void}  \ifdefvoid{\myemptyempty}{Void}{Not void}  \end{document} To turn off my system, I can use one of these three commands:  sudo halt   Or:  sudo poweroff   Or:  sudo shutdown -h now   What are the differences between these commands, or are they all just aliases of each other? How to find all questions that were duplicates of another question? I am interested to see a list of all questions that were closed because being a dup of another question.  I strongly want to research a particular question and reading all the answers inside the dups will help me a lot.  Is there such feature? if not, this is a feature request How does Hextech Crafting work? How do you earn free loot?  What's the deal with essences and why are they so important?  What do the different options mean when dealing with Redeeming Rerolling Disenchanting and Upgrading?  How does it all work? Can I re-create deleted Gmail accounts? A long time ago, I created a Google mail account. I fell for a trap that was common back then (not sure how it is nowadays) and ended up with two Google accounts—one for Gmail (using the Gmail email address I would like to use) and one for everything else (using an email address at an external mail provider).  Hoping that I could associate my Gmail and my actual Google account, I deleted my Gmail account only to discover that deleted account names cannot be used again. So basically my old Gmail account along with the Google email address I would like to use is gone.  My main Google account got assigned a different Gmail account in the mean time.  Do you know if it is possible to re-use my preferred Gmail address? If possible, I would like to assign it to my main Google account. But I'd also be happy to have it as a second Google account, anything is better than the current situation. How do I find out what tool a shortcut is triggering? I used to have problem with connecting two objects, because when I smooth the final object, there was a darker line on the connected parts (for example when I was making head, I've had eyes darker this way). Then I found out that I can get rid of it by hitting Ctrl+N, but I don't realy know what it does. I can just see that the lines are gone. So, what does Ctrl+N do? Using (or not) the word "to" in a sentence ending with "be able"