If matrix $A$ is unitary and $B^2 = A$ then $B$ is also unitary
If matrix $A$ is unitary and $B^2=A$, is $B$ necessarily unitary?
C++ catching all exceptions With proper nouns, we don't use the except for river names, newspaper names, etc.  I want to know why we use the with White House. I mean, under which rule can we categorize it? What could other similar examples for that rule be? Semigroup analogue to the classification of finite simple groups? Is there a semigroup analogue to the classification of finite simple groups?  If so what are some of the major results?  --Edit, reference links--- C++ warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings] Clock time is off on dual boot Dual boot system Windows XP Pro and Ubuntu 12.04.  I have the bios set for the correct time and Ubuntu set for US Eastern time.  Ubuntu will boot up and the time will be off by -4 hours.  If I correct the time in Ubuntu then when I boot up in Windows XP the time will be off by + 4 hours.  This is a fresh install of 12.04. I did not have this problem before reinstalling Ubuntu. How to prove that compact subspaces of the Sorgenfrey line are countable? How to prove that every compact subspace of the  is countable? How do I resize my current ubuntu partition? Is it essential to use comma in a big number? Is it necessary to use comma in a big number? For example, if anyone writes one million four hundred thousand and two as 1400002 instead of 1,400,002 on answer sheet of listening section of IELTS test, will it be considered incorrect?  Thanks in advance. list transparency across non consecutive slides I am looking for a way to get the output of a command when it is run from within a C++ program.  I have looked at using the system() function, but that will just execute a command. Here's an example of what I'm looking for:  std::string result = system("./some_command");   I need to run an arbitrary command and get its output. I've looked at , but I have not found anything that will give me what I need. Let $X$ and $Y$ be topological spaces. A function $f: X \rightarrow Y$ is defined as continuous if for each open set $U \subset Y$, $f^{-1}(U)$ is open in $X$. This definition makes sense to me when $X$ and $Y$ are metric spaces- it is equivalent to the usual $\epsilon-\delta$ definition. But why is this a good definition when $X$ and $Y$ are not metric spaces?  How should we think about this definition intuitively? I'm using Python, and would like to insert a string into a text file without deleting or copying the file. How can I do that? My regex is matching too much. How do I make it stop? I have this gigantic ugly string: J0000000: Transaction A0001401 started on 8/22/2008 9:49:29 AM J0000010: Project name: E:\foo.pf J0000011: Job name: MBiek Direct Mail Test J0000020: Document 1 - Completed successfully  I'm trying to extract pieces from it using regex. In this case, I want to grab everything after Project Name up to the part where it says J0000011: (the 11 is going to be a different number every time). Here's the regex I've been playing with: Project name:\s+(.*)\s+J[0-9]{7}:  The problem is that it doesn't stop until it hits the J0000020: at the end. How do I make the regex stop at the first occurrence of J[0-9]{7}? Recently I answered two questions on SO: The  is a completely trivial answer to a really basic question (kind of "read the manual and follow the one liner example there"). On the other hand, my  is a much more complicated answer that requires much more specialized knowledge of a very specific domain (happens to be related to my PhD research).  Clearly, the first answer could have been given by many SO users - I just happened to be the first to pick up the glove on this question. However, this is not the case for the second answer.  In contrast, when it comes to reputation - the first answer instantly got upvoted (everyone can relate to a simple question/answer), while the second one - I don't believe it will get much upvotes...  So, life isn't fair: for the one answer that really very few people could provide (the second answer) and is much harder to find and get -- is not rewarded, while the trivial answer is rewarded fast and strong...  How can we amend this? How can we encourage rare and specialized answers for difficult and deep questions?  Do we want SO to turn into a pool of trivial and superficial questions?    Update: Thanks to many meta-users who took the time to read through this question and ponder its implication, both answers I used as examples got exposed far beyond their fair-share. So, despite the fact that my original claim that the specialized answer get less reps is no longer valid, this does not change fact that in general my claim is stil valid: specialized answers requiring expert knowledge will recieve less attention at first.    Bottom line: (following my wish to have some sort of ). Indeed it sometimes seems like life isn't fair, but this is only in the short term. In the long run high quality answers do get their proper credit and exposure and their fair share of reputation. The reputation system of SO works quite well balancing and accounting for many factors and parameters. It would require a really strong argument backed up with serious research to change this mechanism.   Thank you all for the lively discussion and for showing me that life is fair after all. Run a Windows Service as a console app Uniform convergence of alternating series Because of past conflicts, I don't believe my advisor will write me a good LOR for postdoc positions. What should I do? I've browsed the forums and found a number of posts that have addressed this issue, but none of the solutions seem to work for me. I have the following script that I just copied from the bibtex home page to get familiar with it. Instead of the citation number I get a question mark. I compile using Latex+Bibtex+Latex+Latex+PDFLatex+ViewPDF just as has been previously suggested and the problem persists.   \documentclass[11pt]{article} \usepackage{cite}  \begin{document}  \title{My Article} \author{Nobody Jr.} \date{Today} \maketitle  Blablabla said Nobody ~\cite{Nobody06}.  \bibliography{mybib} \bibliographystyle{plain} \end{document}   My bibliography (Bib.bbl)  @misc{ Nobody06, author = "Nobody Jr", title = "My Article", year = "2006" }    Looking at previous posts one thing that is concerning is that my .bbl looks empty as shown below. Further, I don't have a .blg  \begin{thebibliography}{}  \end{thebibliography} If you look at this product:    you can clearly see that it is a DVD+R, i.e. once it is written, it cannot be erased/rewritten.  Then what does the "RW" logo (in the lower right corner) mean? I thought it stood for ReWritable, but experimenting with the medium shows that it is not. Word whose form is contrary to its meaning? Is there a word for a word whose form is contrary to its meaning?  For example, "quotidian" is anything but quotidian.