Is apt-file part of apt? I have apt installed by default, but no apt-file.  How about apt-cache? I don't remember whether mine was installed by default or me.
Simple enough question: is there some shell command (or GUI method) I can use that, given the path to a file on my system, tells me what package put it there? Assuming the file did in fact come from a package, that is.  Bonus question: what if it's a file that isn't installed on my system? Is there, say, a website that will let me look up a file and see what packages, if any, provide it?
3 Statements of axiom of choice are equivalent This winter I started to study much harder the set theory and especially the axiom of choice. Unfortunately, I have problems with solving the next exercise:  Prove that the 3 statements of the axiom of choice are equivalent :  1) For any non-empty collection $X$ of pairwise disjoint non-empty sets, there exists a choice set.  2) For any non-empty collection $X$ there is a choice function.  3) For any non-empty set $X$, there exists a function $f:P(X)\setminus\{\varnothing\}\to X$ so that for any non-empty set $A\subseteq X$, $f(A) \in A$. Unexpected gaps in IDENTITY column Can a US citizen leave and enter the US using a foreign passport? How to typeset asymmetrical confidence level limits / uncertainties? Below is an example of an asymmetrical limit (or uncertainty)  How can I typeset this in a \LaTeX equation? Such pair of numbers should be vertically stacked while being vertically center-aligned with rest of the equation. Solution $X^{+Y}_{-Z}$ You can reach this IP address  (if my computer is online). I want to assign a domain to it so I wonder how is that possible when I have no DNS? I do own my domain which is ".com". My IP is static.  Thanks 'innerText' works in IE, but not in Firefox How to check which TLS protocol is using the FUEL-SDK for java How can I stop being prompted to unlock the 'default' keyring on boot? Whenever Ubuntu boots up, a dialogue pops up asking me to unlock my default keyring. Is there some way this can unlock automatically through PAM or some other magical way? Is there ever a right time to upgrade to full frame camera body? Context  I've been shooting with an a6000 (APS_C mirrorless) and I plan to move on up to full frame, preferably mirrorless as well. I'm debating on when to upgrade, and probably don't plan to buy until next year.  I know I'll need to buy new full frame lens.  Question  Is there a "right" time to buy camera bodies, both mirrorless in my case as well as DSLRs? (I've seen the a7rII and like it but there might also be an a9 looming.) I feel that this is like smartphones in which the best time to buy is now as you might always be waiting until the next upgrade.   Related, are full frame bodies discounted during the holiday season or is that limited only to entry level bodies and older full frame bodies?  Related The Matching Problem/Derangements - n letters to n people There are n letters addressed to n eople at different addresses. The n addresses are typed on n envelopes.  A disgruntled secretary shuffles the letters and puts them in the envelopes in random order, one letter per envelope.  Find the probability that at least one letter is put in a correctly addressed envelope. [Hint: use the inclusion-exclusion formula.] What is the probability approximately, for large n ?    My attempt at a solution:  P(all correct) = $\frac{1}{n!}$  P(n-1 correct) = ${n \choose n-1} \frac{1}{n!} = \frac{1}{1!(n-1)!}$  ${n \choose n-1}$ ways of selecting n-1 correct letters.  P(n-2 correct) = ${n \choose n-2} \frac{1}{n!} = \frac{1}{2!(n-2)!}$  ...  P(n-n correct) = ${n \choose n-n} \frac{1}{n!} = \frac{1}{n!(n-n)!} = \frac{1}{n!}$  This all looks ok to me, but I tested this for a case of 4 people, (I think the theoretical value should be $\frac{9}{24}$ but obviously that is not what I got. Can someone correct my logic please? Also, with regards to the hint about inclusion/exclusion - where would that come in?  I read about derangements on Wikipedia but it did not make total sense to me (the derivation).  I would appreciate any advice whatsoever including references to other material. How to convert sshfs command to fstab entry? From another SO , I understand I should create an entry in fstab to permanently mount an access to a virtual machine.  I am not Linux expert. The magic command which allows me to perform this from a terminal is:  sudo sshfs -o idmap=user -o allow_other -o nonempty jverstrynge@devjverstrynge:/home/httpd /home/jverstrynge/httpd   When I check the above SO question, I see an entry looking like this:  /media/mybook/laptop_backup /export/laptop_backup none bind 0 0   Can someone explain how to transform the CLI command into an entry in fstab? I have the following code:  if ($_POST['submit'] == "Next") {     foreach($_POST['info'] as $key =&gt; $value) {         echo $value;     } }   How do I get the foreach function to start from the 2nd key in the array? I had two drives partitioned the same and running two RAID partitions on each.  One died and I replaced it under warranty for the same model.  While trying to partition it, the first partition can only start on sector 2048, instead of 63 that was before. Drive have different geometry as previous and remaining ones. (Fewer heads/more cylinders)  Old drive:  $ sudo fdisk -c -u -l /dev/sdb   Disk /dev/sdb: 2000.4 GB, 2000398934016 bytes 255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000aa189     Device Boot      Start         End      Blocks   Id  System /dev/sdb1   *          63   174080339    87040138+  83  Linux /dev/sdb2       174080340   182482334     4200997+  82  Linux swap / Solaris /dev/sdb3       182482335  3907024064  1862270865   fd  Linux raid autodetect   Remanufactured drive received from warranty:  $ sudo fdisk -c -u -l /dev/sda  Disk /dev/sda: 2000.4 GB, 2000398934016 bytes 81 heads, 63 sectors/track, 765633 cylinders, total 3907029168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000d0b5d     Device Boot      Start         End      Blocks   Id  System /dev/sda1            2048  ...   Why is that? Is "National Socialism" always capitalized? So, I'm writing a paper on the rise of communism in China. At one point I write the following:     "Today, it is well known that communism is responsible for more deaths than even national socialism."   Then, Word corrects it by capitalizing "National Socialism."   Is it always meant to be capitalized? I am simply referencing the ideology, not necessarily the Third Reich. Word didn't bother to correct "communism." I suppose since there was only one instance of Nazism (on a national scale at least) it could be considered a proper noun. Is it ever bad to use \left and \right? For mathematics, is it ever disadvantageous to use \left(  and \right)  in equations?  I can't see any way that doing this would hinder the typesetting, so why isn't () just converted into \left( \right) automatically? This would save a lot of typing.  Cheers! As far as I know, current division for spesific place's formula is: Ix=(Req/Rx)*Isource   However, here,the solution is 3/(3+2+4)*6. How is this a current division ? Can you explain this to me How do I calculate the closest power of 2 or 10 a number is? Empty intersection and empty union I have a file with the lines like below.  title1:A1 title2:A2 title3:A3 title4:A4 title5:A5  title1:B1 title2:B2 title3:B3 title4:B4 title5:B5  title1:C1 title2:C2 title3:C3 title4:C4 title5:C5  title1:D1 title2:D2 title3:D3 title4:D4 title5:D5  How can I achieve this?   title1    title2     title3    title4 A1         A2         A3         A4 B1         B2         B3         B4 C1         C2         C3         C4 D1         D2         D3         D4 With a firmware password set on a Retina MacBook Pro, what are recovery options? I am considering setting a firmware password on my Retina MacBook Pro for security reasons. If I do this and later lose the password (or other such extenuating circumstances), how can the data be recovered? Is it even possible?