Weird unpacking in list comprehension
What does ** (double star/asterisk) and * (star/asterisk) do for parameters?
A classic exponential inequality: $x^y+y^x>1$ This is a classic problem, but I haven't seen it on the site before.     Suppose $x$ and $y$ are real numbers that both lie in the interval   $(0,1)$. Prove  $$x^y+y^x&gt;1.$$   The following spoiler box contains a hint that indicates the solution I know. Does anyone know a more natural solution?       Use Bernoulli's inequality to show $$x^y\ge \frac{x}{x+y}.$$   Edit: I recently learned the source is the 1996 French math olympiad. My bibliography (made with biblatex) has all items close to each other. I would like to introduce some space between them, e.g. half a line.  How can I do this? What is the time span of The Last Jedi? Is it poor form to switch accepted answers? I had a question of the form "does something like X exist?" Someone wrote a response to say that, No, X does not exist, but I could write it if I liked. I had suspected as much, so I marked his answer as the accepted answer. Today someone actually posted the code to do X for me, and I feel that the new poster deserves the "Accepted Answer" checkmark.  Is it poor form for me to pick a new Accepted answer? Does the original answerer get penalized in terms of reputation?  While the original responder's answer was accepted at the time, I feel this new answer is really more helpful.  Edit: Which of these responses should I accept? What does the notion of a single accepted answer mean with a question that is subjective that could have multiple "right" answers? Suppose we have a magnetic field directed into the computer screen. Assume that there is no gravitational field. Now suppose we have a stationary positively charged particle in the magnetic field. The magnetic force is given by $$\mathbf{F}=q\mathbf{v}\times\mathbf{B}$$  Since $\mathbf{v}=0, \mathbf{F}=0$.  Now pick a reference frame moving to the left with constant velocity. In this frame, the particle is moving to the right with constant velocity. So, the magnetic force is directed upwards.  From what I've learnt in physics, forces are independent of choice of reference frames as long as the frames are inertial. But in the 2 inertial reference frames I have chosen, I get 2 different magnetic forces. How do we reconcile this? Received W-2 but was never paid I just now received a W-2 from a company that I worked for 3 days as a contractor. I had to leave country for 2 months due to a family emergency. Since the employment duration was very short, I was not paid. I was told that they don't want to charge the client because 3 days is not enough contribution.  Since I had to leave country the same day, I did not argue with them and told it's okay if they feel right.  Now I have a W-2 from them saying they have paid me about $1500. I contacted them but I have not received any reply yet.  I just want to be prepared. What can I do here? Threshold Secret sharing - How to create a shared secret from pre existing secret parts? In usual $(t, n)$ secret sharing schemes, a secret $S$ is split into $n$ parts so that any $t$ out of $n$ parts reconstruct the original secret. So, suppose that there is a group of $n$ participants each one has a secret $x_i$ ($x_i$ may be its private key). My question is, is it possible to create a secret $S$ using the prexisting secrets $x_i$ ($i=1...n$) so that with any $t$ out of $n$ from these secrets ($x_i$) we can find the secret $S$? $\int_{0}^{\infty}\frac{\sin^{2n+1}(x)}{x} \mathrm {d}x$ Evaluate Integral Here is a fun integral I am trying to evaluate:  $$\int_{0}^{\infty}\frac{\sin^{2n+1}(x)}{x} \ dx=\frac{\pi \binom{2n}{n}}{2^{2n+1}}.$$  I thought about integrating by parts $2n$ times and then using the binomial theorem for $\sin(x)$, that is, using $\dfrac{e^{ix}-e^{-ix}}{2i}$ form in the binomial series.  But, I am having a rough time getting it set up correctly. Then, again, there is probably a better approach.   $$\frac{1}{(2n)!}\int_{0}^{\infty}\frac{1}{(2i)^{2n}}\sum_{k=0}^{n}(-1)^{2n+1-k}\binom{2n}{k}\frac{d^{2n}}{dx^{2n}}(e^{i(2k-2n-1)x})\frac{dx}{x^{1-2n}}$$  or something like that. I doubt if that is anywhere close, but is my initial idea of using the binomial series for sin valid or is there a better way?.  Thanks everyone. Why do I need to type `./` before executing a program in the current directory? While executing a C program, a.out, using the Ubuntu terminal, why do I always need to type ./ before a.out, instead of just writing a.out? Is there solution for this? Someone is offering to pay me in a sort of sugar daddy/sugar baby arrangement. They want to make online deposits to me, and they're asking me for my online banking username and password. Is that information alone enough for them to be able to take my money out of my account, or am I safe? Since the last update (v1.0.85), I am getting all the question pages blank on the Android app. For those who are confused with the image, I'm using RtL (Right-to-Left) layout.        If I scroll down (quite a bit) I can see the question. But even then I cannot see the question title, the related comments or answers.         App Version: 1.0.85 Device Manufacturer: LGE Device Model: LG-D620   OS Version: 5.0.2 (152541901f156) Disable window animations when the menu option is missing? How do I set Window animation scale and Transition animation scale to Animation off when  the option to do so is not available on my ROM (though it ought to be). Specifically it should be under Developer options in Settings but all of the User interface options are missing. In what kind of rings a divisor of a product is a product of divisors? In a , if $a|bc$, then $a$ can be written as $a = a_1a_2$ so that $a_1|b$ and $a_2|c$.  Is this property of a commutative ring strictly weaker than the property of being a UFD?  If so, does it have a name, or is it equivalent to some other well-known property? Prove that ${{n}\choose{k}} = {{n - 2}\choose{k}} + 2{{n - 2}\choose{k - 1}} + {{n - 2}\choose{k - 2}}$. I'm looking for some guidance in solving this. I have read through my text multiple times trying to find something similar to this and I'm coming up with nothing. I'm not really sure where to start on solving this problem.  The question simply states     Prove that ${{n}\choose{k}} = {{n - 2}\choose{k}} + 2{{n - 2}\choose{k - 1}} + {{n - 2}\choose{k - 2}}$.   I'm very new to binomial coefficients, and extremely lost. For a finite set $S$ there are $\vert S\vert!$ orderings of its elements.  What is the cardinality of all orderings of $\mathbb{N}$?  What would $$\vert \mathbb{N}\vert!$$ mean?  Is it $\prod_{n\in\mathbb{N}} \aleph_0=\aleph_0^{\aleph_0}=\aleph_1$?   says the "equivalence classes of well-orderings of the natural numbers" has cardinality $\aleph_1$.  But I can't put together in my mind the connection between well-orderings of $\mathbb{N}$ and all orderings of $\mathbb{N}$.  (Are there non well-ordered orderings of $\mathbb{N}$?)  This leads to wondering what the cardinality of all orderings of $\mathbb{R}$ is.  (Actually my thought process went in the other direction, from $\mathbb{R}$ to $\mathbb{N}$.)  I think knowing the answer to the above question will teach how to determine what $$\vert \mathbb{R}\vert !$$ means, if anything.  I will be happy if you assume the continuum hypothesis to be true for the purposes of this question, but any level of completeness is welcome. Ways to give users some specific education about question quality and topicality Important: This question is being asked here, and not on the Programmers Meta,  because I believe that several SE sites suffer from this same, specific problem.    On Programmers, I see a pattern emerging.   New User sees the "Programmers" site title, and asks their incomplete, "fix my broken code" question. Community members comment that their question is off-topic, and recommend Stack Overflow.  New User says "thanks" and leaves, leaving their undeleted question for the community to clean up.    What seems clear to me is that:   New User has never seen the "What kinds of questions can I ask about here" page, or if they have, they've clicked through it without reading it. New User doesn't know how to move their question to the right place properly  (i.e. post on new site, delete from old site). Community cleanup of such questions is onerous.  The moderators on Programmers, following the principle that the community should moderate itself for the most part, are not proactive about removing such questions unless they're especially egregious. Migration is even more onerous.   OK, so we have the .  Here's what it says about topicality, about halfway down the page:    Note to those who are confused about Programmers' site scope: it's all right there, in black and white.  However, I do notice a problem.  It's circled in red.  That's our fault, the fault of the Programmers community.  What we really meant to say was "Don't ask your code troubleshooting questions here; those belong on Stack Overflow."  Coding tools deserves its own bullet.  We should fix that.  However, what are the chances that the user is actually seeing this, and evaluating whether or not they should ask their question based on this?  So here's my question, in two acts:  ACT I:  Is there a way to highlight the pain points of a particular site to new users specifically, so that we can be very clear that we don't want those questions that are clearly and unambiguously off-topic on our site, before they ask their question?  ACT II: Failing that, is there a way that we can fast-track the removal of such questions so that they no longer pollute our front page? Is the empty set a subset of itself? How do you rotate a two dimensional array? Inspired by , say you have a 4x4 two dimensional array, write a function that rotates it 90 degrees. Raymond links to a solution in pseudo code, but I'd like to see some real world stuff.  [1][2][3][4] [5][6][7][8] [9][0][1][2] [3][4][5][6]   Becomes:  [3][9][5][1] [4][0][6][2] [5][1][7][3] [6][2][8][4]   Update: Nick's answer is the most straightforward, but is there a way to do it better than n^2? What if the matrix was 10000x10000? Where did the name "Stack Exchange" come from? I get Stack Overflow (which I'm guessing was the first site?) and Super User, Code Review, and the other sibling site names make sense to me.  But I've never heard of a stack exchange before.  Is a stack exchange a real thing, or is this site's name a combination of Stack Overflow and an exchange of ideas? How can I visualize or simulate the effect of different focal lengths? I have seen many camera review sites illustrate the effect of using different focal lengths on the same photograph using frames. There are also similar illustrations to compare different sensors (). I find this kind of visualization to be very useful in comparing the actual effect of the longer focal length\different sensor size. Of course the ability to do a wider focal length visualization would also be equally useful, but that's not possible.  Is there any ready-made software or plugin that enables this? If not, is there any simple technique to visualize the effect of longer focal lengths on an image (one would of course have to use the zoom information in the image EXIF data to accurately represent this)? All I can think of is to use some trigonometry to do the necessary calculations for the frame sizes for cropping.