Is $\arctan2$ irrational?
Show that $\arctan(n)$ is irrational for all $n \in \mathbb{N}$
Linear functional on a Banach space is discontinuous then its nullspace is dense. Summary table with a field that shows components of each summarized record Some time ago, I baked a cake (Sachertorte to be exact). The taste and texture was fine, so my recipe is okay.  My biggest issue was the shape. In the middle it was really a lot higher than on the sides. I would like to redo it in the near future, but preferably with a flat(ter) surface. (Especially since I put icing on top and I don't want it to drip off this time.)  Anyone knows the cause of my problem, or even better a solution? I think I put enough butter on the side of my springform pan, in case this is an option. 1.7.4 Problem with mobs spawning I have just updated to Minecraft 1.7.4 and now all of a sudden there are barely any mobs spawning.  I checked to make sure that I was in normal difficult and I saw 1 creeper but that is all.  Also I tried different difficulties. Another thing - mobs seem to to spawn normally in the nether and all other mobs except aggressive mobs spawn like they should.  Please if you know how to fix this, please help! How to make 7-zip do a whole bunch of folders I got a bunch of pictures that I had to crop into 800x600 pixels. That was easily done, but now I have to upload them so the family can see them all.  Thing is, this is 500MB in pictures. I decided to simply zip the separate folders, which each contain an almost equal amount of pictures. This way I can upload a couple each day. Doing this manually is a very long and hard job. I wonder if there is a way to make 7-zip handle each folder individually?  I think I'll need a batch file to do it, but I'm not good with that. I've put everything under one folder. In the various subfolders is where the pictures are located. What I need is for the contents of that folder to be zipped. I'm not sure if I can just zip the folder along with it. I know PHP has a zip module, I've just never worked with it, so I'm not sure whether it can handle the fact that the content of the zip is a folder which contains the items, instead of just the items. GNOME 3.26 - Clicking one window brings another in the foreground (Ubuntu 17.10) I'm on Ubuntu 17.10 with GNOME 3.26.  Often I have windows tiled on the left and right side of the screen. A typical setup is to have a browser and text editor on the left, a PDF reader and terminal on the right.  Something I've seen happen very often: I'm reading the PDF on the right, having the window in focus. The text editor on the left. When I click on the text editor to write something, it brings forward another window on the right (say the file browser), covering the PDF reader.  This seems to have something to do with the Alt-Tab view history.  My question is: Is it possible to remove the automatic bring-to-front of windows? I don't understand why unrelated windows are brought to the front when I click on another application. That's kind of a recursive Google Search that should be self-explanatory. It did take me some time to tweak the sentence and trying to find a number which would correspond precisely, the reason why I changed it to "hundreds" instead! :P  If you have used Google long enough you certainly have stumbled on situations similar to this, many times. Whenever it shows less than 10 pages it's quite easy to see it. The point is: the number of results on any page except the last one seems like a terrible estimate.  What's even weirder,  the estimate suddenly becomes much better and almost exactly the same on all pages than it is on the last page - the only page that's always correct.  So, anyone knows why? How do I define global variables in CoffeeScript? What tips and advice do you have for photographing the Aurora Borealis? In Monopoly, Is it OK for a third party to make a trade with a player who is about to lose? I play with some serious board gamers, but we have neglected Monopoly for a number of years, so our knowledge is mostly based on high school &amp; house rules.  We played last week and enjoyed it, but there was a piece of contention. There are times where we decide that we don't like one of our friends for some reason and don't want them to win (i.e. we landed on their property a bunch, or they refused to make a deal, etc.).  So when player 1 has some property and player 2 lands on it and cannot pay the rent their assets (houses/hotels get liquidated), their property gets transferred to the other player. (Please correct me if I'm wrong.) In this case, though, player 3 "traded" the amount of money owing for a piece of property (way overpaid). In this case they did it so that player 1 would not get the properties. Player 2 had no chance of winning the game (all properties mortgaged, no cash to speak of and many of the other properties with 3+ houses/hotels on them).  To summarize: Is it OK for a third player to purchase/trade property or cash to/from a player who is about to lose? Tokenizing strings in C I have been trying to tokenize a string using SPACE as delimiter but it doesn't work. Does any one have suggestion on why it doesn't work?  Edit: tokenizing using:  strtok(string, " ");   The code is like the following  pch = strtok (str," "); while (pch != NULL) {   printf ("%s\n",pch);   pch = strtok (NULL, " "); } In , someone suggested in a  that I should not cast the result of malloc. i.e., I should do this: int *sieve = malloc(sizeof(int) * length);  rather than: int *sieve = (int *) malloc(sizeof(int) * length);  Why would this be the case? 2D inhomogeneous biharmonic equation Which shells don't support dollar-parenthesis expansion, and demand backticks? lstlisting - line number gaps I am using the document class article. Once I place a part in the document, all subsequent sections belong to the part automatically. How can I reset a section such that it does not belong to a part?  The following sample demonstrates what I want to achieve:  \section{Introduction}  \part{Part 1} \section{Section 1 belonging to part 1} \section{Section 2 belonging to part 1}  \part{Part 2} \section{Section 1 belonging to part 2} \section{Section 2 belonging to part 2}  % should not belong to Part 2 \section{Conclusion} I am writing an article in English, with some pages in Russian.  \documentclass[12pt]{article}  \usepackage[T1,T2A]{fontenc}  \usepackage[utf8]{inputenc}  \usepackage[russian,english]{babel}  \usepackage{newtxmath} \usepackage{newtxtext} \begin{document}  hello \textbf{hello}  \selectlanguage{russian} привет \textbf{привет}  \end{document}   Output:  hello hello привет привет  I am using \selectlanguage{} to switch between languages when needed.  However, I noticed that when I try to use \textbf{} when in Russian language mode, it does not work because of newtxtext, which I am using for math formulas.  Does anyone know how to solve this problem?  Thank you. There are $k$ penguins, $k\ge 3$. They are all different heights. How many ways are there to order the penguins in a line, left to right, so that we cannot find any three that are arranged tallest to shortest (in left to right order)? The penguin triples do not have have to be adjacent.  This problem is courtesy of someone I know only as "DaMancha." How to match all occurrences of a regex Is there a quick way to find every match of a regular expression in Ruby? I've looked through the Regex object in the Ruby STL and searched on Google to no avail. Why does magnet attract iron but not other metals? While searching, i found this page:  but it does not have full explanation. So Please tell full explanation of why this happens?