How can I scan for possible viruses on my Ubuntu system?
How do I scan for viruses with ClamAV?
How to set JAVA_HOME to point to a JDK installation? I installed sun-java6-jdk.  I need to find its home directory. JAVA_HOME must point to a JDK installation, not JRE. Proof of a combinatorial identity: $\sum\limits_{i=0}^n {2i \choose i}{2(n-i)\choose n-i} = 4^n$ Possible Duplicate:          This was part of a homework assignment that I had, and I couldn't figure it out. Now it is bugging me. Can anyone help me? Although a proof would be nice, I wouldn't mind a push in the right direction.   $\displaystyle\sum_{i=0}^n {2i \choose i}{2(n-i)\choose n-i} = 4^n$ I've been studying about the command line and learned that | (pipeline) is meant to redirect the output from a command to the input of another one. So why does the command ls | file doesn't work?  file input is one of more filenames, like file filename1 filename2  ls output is a list of directories and files on a folder, so I thought ls | file was supposed to show the file type of every file on a folder.  When I use it however, the output is:      Usage: file [-bcEhikLlNnprsvz0] [--apple] [--mime-encoding] [--mime-type]         [-e testname] [-F separator] [-f namefile] [-m magicfiles] file ...     file -C [-m magicfiles]     file [--help]   As there was some error with the usage of the file command Assume: $p$ is a prime that satisfies $p \equiv 3 \pmod 4$  Show: $x^{2} \equiv -1 \pmod p$ has no solutions $\forall x \in \mathbb{Z}$.  I know this problem has something to do with Fermat's Little Theorem, that $a^{p-1} \equiv 1\pmod p$. I tried to do a proof by contradiction, assuming the conclusion and showing some contradiction but just ran into a wall. Any help would be greatly appreciated. Example of non-isomorphic structures which are elementarily equivalent I just started learning model theory on my own, and I was wondering if there are any interesting examples of two structures of a language L which are not isomorphic, but are elementarily equivalent (this means that any L-sentence satisfied by one of them is satisfied by the second).  I am using the notaion of David Marker's book "Model theory: an introduction". Does Mathematica have a "MATLAB Builder" equivalent? Seeing close-vote details if I've already voted If I've already voted to close a question, it would still be nice to see the details of others' votes — the suggested migration if it's being marked as off topic, or the suggested duplicate if it's being marked as an exact duplicate, for instance. Instead, I only see "You have already voted to close this question" and the overall category. Debugging a custom-bib bst file that crashes on book items I created my own bibliography file with custom-bib (makebst), but when I run it with a reference to a book I get:  $ bibtex PhD [...normal output] Database file #1: PhD.bib You can't pop an empty literal stack for entry oecd2001brc while executing---line 1504 of file wdsphd.bst   The only thing on that line is a high-level ITERATE call.   The style was created with these options:  %% merlin.mbs  (with options: `head,exlang,annote,seq-no,nm-rvvc,dt-beg,yr-par,xmth,tit-qq,qx,bt-qq,vol-bf,volp-sp,num-xser,pub-date,isbn,issn,doi,english,pp,ord,url,url-nl,nfss,,{}') %% english.mbs  (with options: `exlang,annote,seq-no,nm-rvvc,dt-beg,yr-par,xmth,tit-qq,qx,bt-qq,vol-bf,volp-sp,num-xser,pub-date,isbn,issn,doi,english,pp,ord,url,url-nl,nfss,,{}') %% merlin.mbs  (with options: `tail,exlang,annote,seq-no,nm-rvvc,dt-beg,yr-par,xmth,tit-qq,qx,bt-qq,vol-bf,volp-sp,num-xser,pub-date,isbn,issn,doi,english,pp,ord,url,url-nl,nfss,,{}')   The code for book items looks like:  FUNCTION {book} { output.bibitem   author empty$     { format.editors "author and editor" output.check     }     { format.authors output.nonnull       crossref missing$         { "author and editor" editor either.or.check }         'skip$       if$     }   if$   format.btitle "title" output.check   crossref missing$     { format.bvolume output       new.block       format.number.series output       new.sentence       format.publisher.address output     }     {       new.block       format.book.crossref output.nonnull     }   if$   format.edition output   format.isbn output   format.doi output   new.block   format.note output   fin.entry   write.url }   And this is the entry:  @book{oecd2001brc,  author = {OECD},  doi = {10.1787/9789264193550-en},  isbn = {9789264186903},  publisher = {OECD Publishing},  title = {{Biological Resource Centres: Underpinning the future of life sciences and biotechnology}},  url = {http://www.oecd-ilibrary.org/science-and-technology/biological-resource-centres\_9789264193550-en},  year = {2001} }   Is there a way to get a better stacktrace from bibtex? What I have now doesn 't really tell me what is going on. If it can be fixed simply, help would also be appreciated. How to restore original size and unboot my bootable USB pendrive I recently made my pen-drive bootable with Ubuntu 14.04. But I need to unboot my pen-drive now. I formatted my pen-drive once,But the size of the pen-drive still shows 2.25 MB. Whereas,this is an 8GB pen-drive. How can I get rid of this problem. I'm still using Windows 7. $K\subseteq \mathbb{R}^n$ is a compact space iff every continuous function in $K$ is bounded. I need to prove that $K\subseteq \mathbb{R}^n$ is a compact space iff every continuous function  in $K$ is bounded.  One direction is obvious because of Weierstrass theorem. How can i prove the other direction? I tried to assume the opposite but it didn't work for me.  Thanks a lot. If/Else with Selenium IDE - when confirmation message comes up I have a scenario, in case of the user registration successful, it will display a success message on the next page otherwise an error message shows on the same page. How to automate the test case to return as passed if it is success and failure in case of error message comes up.  Please help me out here. If I upgrade Ubuntu 12.04 to 14.04, will NS2 still be supported?  I am currently using NS2 on Ubuntu 12.04. Why is it that scanf() needs the l in "%lf" when reading a double, when printf() can use "%f" regardless of whether its argument is a double or a float?  Example code:  double d; scanf("%lf", &amp;d); printf("%f", d); Using the Well Ordering Principle to Show that n^3 - n is divisible by 6. I read the following two sources and I think I understand the structure of proofs involving WOP, but I am stuck on the open-ended part where you prove P(n-1) for the  following problem:    Use the well-ordering principle to show that n^3 - n is divisible by 6.    Any help would be greatly appreciated!   Note: After factoring out (n-1)^3 - (n-1) it took the form of n^3 - 3n^2 + 2n and the only difference between that and n^3 - n is "3n^2 - 3n" which I proved was divisible by 6 via induction. Is there a better way to solve this problem?  Edit: , post is useful however I not supposed to use induction for the main part of the proof. Google Maps Location History is showing an incorrect location I have a major problem that I hope someone can help with. On my Google Maps feature under my Location History it shows a location that I was never at at any point, but when my wife happened to see that location she doesn't believe me that the GPS could be wrong and pinpoint that location if I was never there.  I was first wondering myself how could that could be possible if I was never there or my phone was never at that location that was 35 miles away from me and second is there any way I could prove the GPS being wrong? Can I contact Google Maps and can they give an official printout of that certain day and every location I was? I really need to prove my honesty to her and hope there is a way. I have a document divided into \part \chapter \section and \subsection. I have 3 parts and in each part I reset all the counters.  I want that, when I do a crossref to something that is in the 1st part, chapter 3 and section 5, that LaTeX prints something like I-3.5, but  I don't want that in the tableofcontents part that LaTeX prints the part number. For example, what I want is:     Part I      chapter 1 section 1.1 section 1.2      chapter 2   AND NOT     chapter I-1 section I-1.1 section I-1.2      chapter I-2   The command that I've tried   \renewcommand{\thechapter}{\thepart-\arabic{chapter}} \renewcommand{\thesection}{\thechapter.\arabic{section}}   does exactly what I've said  Can anyone help me? Show that any set of 7 distinct integers includes two integers $x$ and $y$, such that either $x-y$ or $x+y$ is divisible by 10 Show that any set of 7 distinct integers includes two integers $x$ and $y$, such that either $x-y$ or $x+y$ is divisible by 10. I'm trying to apply the pigeonhole principle, but haven't been able to come up with a convincing argument.   Though similar to , I think the difference between the two is enough to warrant a second post. Delete all but the most recent n file for each group of files that share the same prefix in a directory My question is a bit different from some older questions simply asking for "deleting all but the most recent n files in a directory".  I have a directory that contains different 'groups' of files where each group of files share some arbitrary prefix and each group has at least one file. I do not know these prefixes in advance and I do not know how many groups there are.  EDIT: actually, I know something about the file names, that is they all follow the pattern prefix-some_digits-some_digits.tar.bz2. The only thing matters here is the prefix part, and we can assume that within each prefix there is no digit or dash.  I want to do the following in a bash script:   Go through the given directory, identify all existing 'groups', and for each group of files, delete all but the most recent n files of the group only. If there are less than n files for a group, do nothing for that group, i.e. do not delete any file for that group.   What is a robust and safe way of doing the above in bash? Could you please explain the commands step-by-step? I have a Asus ROG G551VW laptop and I'm trying to install Ubuntu 16.04 on my laptop, but when i try to load the installer, my laptop just freezes and its fan starts working for no reason. I have tried to install Ubuntu 14.04 on my laptop and the installation went smoothly. What should I do if I want to install Ubuntu 16.04 on my laptop?  Any help would be greatly appreciated. My "network reputation" graph does not accurately reflect my accounts