Example of an interesting topological space that doesn't have a metric
Non-Metrizable Topological Spaces
Do images need a border around them? When rolling percentages, do 1d100 and two d10s (percentiles) share the same probabilities? I know d100s are shunned because they take too much time to roll, and 1d10+1percentile is really fun, but do they share the same probabilities? Is it better to use a (digital) d100?  Also, do d100s have 0? You can't roll a 0 with percentiles, I think. If I want to make a backup of everything I have done since the fresh install of Ubuntu, what are the possible options? What all should I backup? I want to get all the settings that I changed, all the packages I installed, etc. Google Chrome error: Error initializing NSS without a persistent database It was working properly before, suddenly it stopped working. When I tried to open by clicking on its icon, but nothing happens.  As already here are many questions related to this, but none of them are working for me. I already checked  and .  I uninstalled Chrome by following the instructions from .  sudo apt-get purge google-chrome-stable rm ~/.config/google-chrome/ -rf   Again I installed Chrome by:  sudo apt-get install google-chrome-stable   But the problem is still thesame.  When I enter google-chrome in terminal I get following error.  [12289:12323:0723/014456:ERROR:nss_util.cc(744)] Error initializing NSS with a persistent database (sql:/home/maddy/.pki/nssdb): libsoftokn3.so: cannot open shared object file: No such file or directory [12289:12323:0723/014456:ERROR:nss_util.cc(212)] Error initializing NSS without a persistent database: NSS error code: -5925 [12289:12323:0723/014456:FATAL:nss_util.cc(214)] nss_error=-5925, os_error=0 Why doesn't C3PO recognize Leia in R2's recorded message? If an polynomial has a complex root, is it necessary that the conjugate of that root is also a root of the polynomial? I am not sure about this. Please comment on this. I used an SRTM DEM to create a hillshade in QGIS 2.2.0. However, the resultant hillshade seems to be vertically exaggerated. Also, changing the settings for scale and z-factor does not have any effect on the resultant hillshade. I have tried both options in QGIS, Analysis-> DEM (Terrain models) and Terrain analysis -> Hillshade. Both methods gave the same results.  Is this an isolated incident, a bug, or am I missing something? MWE:  \documentclass{minimal} \usepackage{commath, tikz} \begin{document} \begin{tikzpicture} \node {$:$}; \end{tikzpicture} \end{document}   When I compile this, pdfTeX enters an infinite loop. Why? Ok, I just bought a brand new original iPad. Sounds impossible, right? Well, we just opened the box, and it is not even charging. There is no indication that this iPad even works even though it is technically "new." Is this something that Apple will need to fix or do I just need to let it sit on the charger overnight and hope it wakes up from a 2 year sleep in its box? Separator between command list and } .php files are downloaded instead of being parsed by Apache Alt Tags Missing from code In what situations is it more appropriate to use an HTML IMG tag to display an image, as opposed to a CSS background-image, and vice-versa?  Factors may include accessibility, browser support, dynamic content, or any kind of technical limits or usability principles. None of the physics sensors in my game work, I'm trying to create an AI man that chases after a player, but for whatever reason, he just won't sense the player, I've tried copying and pasting the property name just to be sure, but that's not it. Rather than rephrasing my question, let me describe to you the desired user-case:  I create a short shell-script to run command "gnome-terminal --someoptionflagname 'my text to be posted'", and execute this script.  Gnome-terminal pops up, with command-line prompt followed by my text.   ie: fields@mycomputer:/$ my text to be posted  Can this be done? The following quote from  assumes "the URL" comes from somewhere and uses it to restrict the Host header. Where does "the URL" come from? Is it from the first line of a HTTP request (e.g. after GET), or from the input to a web client (e.g. an argument to curl, or the input in the address bar of a web browser)? Thanks.     The Host header specifies the Internet host and port number for the   resource being requested, as obtained from the original URL:  Host = "Host" ":" host [ ":" port ]       In particular:      • If the Host header does not contain a port, the default port for the   scheme is assumed.      • If the URL contains an IP address, the Host header should contain   the same address.      • If the URL contains a hostname, the Host header must contain the   same name.      • If the URL contains a hostname, the Host header should not contain   the IP address equivalent to the URL’s hostname, because this will   break virtually hosted servers, which layer multiple virtual sites   over a single IP address.      • If the URL contains a hostname, the Host header should not contain   another alias for this hostname, because this also will break   virtually hosted servers. As a grad student, I just find it tremendously frustrating when emails are ignored by faculty (both at my institution and at other places). Is this acceptable? I'd be content with a simple response with one line along the lines of "I have read this email and am busy right now, will respond in X days when I can write a more detailed email." I understand that, as a first year student in my field, I'm not really in a position to request anything of anyone, but it just seems like common decency.  Instead, I never hear back, as if my email has been jettisoned off into oblivion. Changing plurality in parentheses If a set of parentheses lies between a subject and its verb, and the parentheses contain an substitutive subject whose singularity/plurality disagrees with the original subject, whose singularity/plurality should be chosen for the verb?  In other words, in the following example, should "questions" (and its verb "are") be singular, or should they remain plural as shown?     Many (if not every) questions on this StackExchange are answered.   My intuition tells me that the two words in question should remain in plural forms, since the text in parentheses only interrupts the sentence (and the sentence would be grammatically incorrect if everything in parentheses were removed and the words were in singular form).  On the other hand, when read aloud (assuming one reads the text in parentheses), this has an uncomfortable sound to it, and I've seen others write in what would be the above example's singular-form case, so I'm curious to find out which is correct.  And, thinking about it, I suppose the same question would apply when commas are used in place of parentheses. How to run scripts on start up? states that if $f:X \rightarrow Y$ is a morphism of ringed space, $G$ is a locally free $O_Y$-module, then $f^*G$ is a locally free $O_X$ module.     Suppose that $G$ is a locally free $O_Y$ module, hence it is a free $O_Y|_U=O_U$ module. We have an induced map  $$f^{-1}(U) \rightarrow U$$ given by restriction of morphism of ringed spaces.   Hence, as $\bigoplus O_U \simeq G|_U$, $f^*:Mod(O_U) \rightarrow Mod(O_{f^{-1}(U)})$ is functorial, $f^*(G|_U) = (f^*G)|_{f^{-1}(U)}$, we have isomoprhism,  $$ \bigoplus O_{f^{-1}(U)} \simeq (f^*G)|_{f^{-1}(U)} $$