Equivalent implementation of Array.prototype.map using for loop
Why is using "for...in" for array iteration a bad idea?
Special Relativity - Regarding the Simultaneity of Events During the Train Paradox Large braces for specifying values of variables by condition Combine the output of two commands in bash Is it possible to combine output from these two commands?  node ~/projects/trunk/index.js  python ~/projects/trunk/run.py run   Neither command exits so I'm not sure how to do this. Helping someone climb I know this is kinda stupid but what is the word for "helping someone climb by allowing him to stand on your hands" (to allow him/her see above some wall or climb something)? Community isn't on ~15 sites! I was looking at the Community user's profile, and I noticed that there was about 15 sites missing in the "accounts" tab. There's a little over 120 sites on SE, and, there's about 15 sites missing from this count. Why is this happening?    Additionally, clicking on view more just shows one account, on Area51: Find a formula for a sequence $\{\sqrt{3},\sqrt{3\sqrt{3}},\sqrt{3\sqrt{3\sqrt{3}}},...\}$ I have a lot of filesystems:   / on a PCI-E SSD swap on a SATA SSD /media/ned is a RAID5 array /tmp lives on RAM Parts of /home/oli are symlinked and bind-mounted in from ned I also have /media/jeff/ which is RAID1 that I store backups and bind-mount ~/.wine in off.   It's actually a lot more complicated than that. There are all sorts of extra symlinks that I need to untangle in the long run but for now I just need a nice way of taking a path and finding out where it physically lives. This one-liner removes duplicate lines from text input without pre-sorting.  For example:  $ cat &gt;f q w e w r $ awk '!a[$0]++' &lt;f q w e r $    The original code I have found on the internets read:  awk '!_[$0]++'  This was even more perplexing to me as I took _ to have a special meaning in awk, like in Perl, but it turned out to be just a name of an array.  Now, I understand the logic behind the one-liner:  each input line is used as a key in a hash array, thus, upon completion, the hash contains unique lines in the order of arrival.  What I would like to learn is how exactly this notation is interpreted by awk. E.g. what the bang sign (!) means and the other elements of this code snippet.  How does it work? Is there a device that could measure the speed of time? Is there (or can there be) a device that could measure the speed and acceleration of time? I am getting really confused now. I installed Tex Live 2012 on my Xubuntu 12.04 with a backport and I installed TexMaker.  I could user PdfLatex right away and it generated everything I needed except my bibliography. I read that Tex Live 2012 comes with biblatex so I just changed the bibtex command in TexMaker from "bibtex" to "biblatex". However, that does not exist. So I did  sudo apt-get remove biblatex sudo apt-get install biblatex   The package is installed but I don't find the binary. Using bibtex the whole thing crashes. Which does not surprise me since I want to userbiber:  \usepackage[backend=biber]{biblatex}   Btw does biber come with biblatex? So far I couldn't get any clear explanation what biber and biblatex are to each other.  EDIT: I had to remove texlive completely and install it with the install script form . Apparently the newest version of biber does not work with the older version of biblatex I had. I'm on SO pretty much every day researching something to do with programming, and over the last month or two, I find I'm growing frustrated and a little disgusted at how many interesting questions have been closed as "not a good fit" or "too subjective".  I think there is a confusion between "subjective" and "calls for judgement". To me one of the most valuable things about SO is the tremendous breadth and depth of experience of the members, and experience translates into smart decisions and advice, and that advice cannot always be asked for, or expressed in terms of, bald facts and data.  It's going to be 'subjective'.  I don't think SO should be Wikipedia. I think that if I could ask a question to a group of skilled programmers sitting around a table at lunch, and get interesting, valuable answers, then I don't care whether the question or the answers are 'subjective', I think that question should equally well be fair game for Stack Overflow.  I would like to see a mechanism whereby people who vote to close a question lose reputation when somebody expresses interest in that question or its responses.  How can I, or can I, influence this aspect of SO? Compare using Thread.Sleep and Timer for delayed execution I have a method which should be delayed running for a specified amount of time.  Should I use  Thread thread = new Thread(() =&gt; {     Thread.Sleep(millisecond);     action(); }); thread.IsBackground = true; thread.Start();   Or  Timer timer = new Timer(o =&gt; action(), null, millisecond, -1);   I had read some  about using Thread.Sleep is bad design. But I don't really understand why.  But for using Timer, Timer has dispose method. Since the execution is delayed, I don't know how to dispose Timer. Do you have any suggestions?  Or if you have alternative codes for delayed execution are also appreciate. How do I connect to a WPA wifi network using the command line? So basically, I'd like to use iwconfig to connect to my wifi network when I'm not inside X. But I just don't see a way to do it in the man page. Any idea? In Europe usually you don't need to go through immigration to change planes (unless you are entering/exiting Schengen). Is it the case in the US as well? May I catch a connecting flight on one of the US airports if I don't have US visa? I'm here with weird stuff again.  How can i continue numbering while changing numbering style to Arabic from Roman? For example let's assume I have total of 7 pages and I want to number the first 3 of them as : i,ii,iii; then I change back to Arabic again and continue counting as 4,5,6,7. Show lim sup (an) = lim inf (an) for increasing for increasing sequence of subsets. Is it possible to programmatically stop and start ArcGIS Server map services using Python? Let $A$, $B$ be two reduced $k$-algebras. Then if an element of the form $$\sum a_{i}\otimes b_{j}$$ is nilpotent, we can compose it with any $k$-homomorphism $f$ from $A$ to $k$ to get a homomorphism from $A\otimes B$ to $B$. This map's image is $$\sum f(a_{i})\otimes b_{j}$$must be nilpotent as well. So if we assume $b_{j}$ is linearly independent in the first place, we may reason that $f(a_{i})=0$. This showed that $a_{i}$ are in the Jacobson radical of $A$. However, we only know $\mathrm{Nil}(A)=0$, and it is not clear to me how to pass from the Jacobson radical to the nilradical without using some commutative algebra machinery.   Here is what I think that might work. If $A$ is of finite type, then by Nullstellensatz we can assert the above is true. But if $A$ is not of finite type, then I can write $A=k[x_{1},...,x_{n}][X]$, where $n$ is the transcendence degree of $k(A)$ and $k[X]$ is finite over $k$. Then I should be able to pass from $k[X]$ to $A$ by inductive argument on the transcendental degree of $k(A)$, since prime ideals are maximal in a UFD (I am working with $k[x]$ by introducing $[x]$).   The proof I have for the case of finite type is not satisfying. Given $I\subset k[X]$, using Nullstellensatz one can show that $$I_{X}V_{X}[I]=\sqrt{I}$$ where $V_{X}[I]$ is the set of all points in $X$ on which $I$ vanishes, and $I_{X}(V_{X}[I])$ be the ideal in $k[X]$ which vanishes on $V_{X}[I]$. Granting this, let $I=(a_{i})$, then we want to show $I=0$, which is $V_{X}[I]=X$. This follows since if $U\subset W$, then $V_{X}[U]\supset V_{X}[W]$. Since $V_{X}[I]\supset V_{X}[m_{x}]$ for all maximal ideal corresponding to points, it must be $X$. This proof is unnecessarily winding by using the ideal-variety correspondence. Ideally I should be able to construct a pure algebraic proof.   The thing not clear to me is whether the above strategy really works. Namely I am not sure if I can really induct on the transcendental degree of $k(A)$. To make matters simple assume we showed the statement holds for $A$ with transdental degree $&lt;n$. For $A$ with transdental degree $n$ we can thus write it as $k[A'][x]$. Then any maximal ideal $m'$ of $k[A'][x]$ must correspond to a maximal ideal $m=m'\cap k[A']$ in $k[A']$. But it seems not possible to show that any prime ideal is maximal. Indeed considering the simple example of $k[x,y]$, where $(x)$ is a prime ideal but not maximal since $k[x,y]/(x)=k[y]$ is not a field. The problem is in the inducting process the base ring is not neccessarily a field, and so this strategy cannot work.   I am thinking maybe I can show $m'=m[f(x)]$ with $f(x)$ some irreducible polynomial in $k[A'][x]$. Because we know $k[A'][x]$ is noetherian by Hilbert's basis theorem, so in particular $m'$ must have a finite generating set. And we can reduce the number of irreducible polynomial to 1 since $m'$ is a maximal ideal. But I still do not know how to use this to finish the proof. Does mass distribution/center of mass affect free fall? An everyday is example would be cars. If you were to drop a car, not taking air resistance into account, would a front-heavy car tumble forward as it fell? And a car with a perfect 50/50 front/rear weight distribution fall straight? Does mass distribution/center of mass affect free fall? Or would they both fall straight down without tumbling? Can you explain why please? $\lim_{x\to 0} \frac{\sin x - x}{x^2}$ without L'Hospital or Taylor