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I have a question, I think it concerns with field theory.     Why the polynomial $$x^{p^n}-x+1$$ is irreducible in ${\mathbb{F}_p}$ only when $n=1$ or $n=p=2$?   Thanks in advance. It bothers me for several days. Is commitment necessary to participate in beta (as of June 2015)? There's this proposal for a new S.E. site which is about to enter the beta phase. It reads  This proposal is in: Commitment A successful site needs people to commit to use it. This proposal is 100% complete. Committed users will be invited to the private beta soon.  I'd like to participate in the beta but I don't want to commit (due to a full name being required). Will I be unable to participate in the beta if I don't commit? Shadow Incorrect at Bottom of Edge Finding the maximum likelihood estimators for this shifted exponential PDF? Consider a random sample $X_1, X_2, \dots, X_n$ from the shifted exponential PDF $$f(x; \lambda, \theta) = \begin{cases}\lambda e^{-\lambda(x-\theta)} ;&amp; x \geq \theta\\                     \theta ; &amp;\text{Otherwise}\end{cases}$$ Taking $\theta = 0$ gives the pdf of the exponential distribution considered previously (with positive density to the right of zero). a. Obtain the maximum likelihood estimators of $\theta$ and $\lambda$. I followed the basic rules for the MLE and came up with: $$\lambda = \frac{n}{\sum_{i=1}^n(x_i - \theta)}$$ Should I take $\theta$ out and write it as $-n\theta$ and find $\theta$ in terms of $\lambda$? What's up with the operating voltages 5 V, 3.3 V, 2.5 V, 1.8 V, etc.? There was a post this morning asking about how many people disable JavaScript. Then I began to wonder what techniques might be used to determine if the user has it disabled.   Does anyone know of some short/simple ways to detect if JavaScript is disabled? My intention is to give a warning that the site is not able to function properly without the browser having JS enabled.   Eventually I would want to redirect them to content that is able to work in the absence of JS, but I need this detection as a placeholder to start. Can moving tables to another MySQL database help performance? I want to know if I using different databases can help performance.  I have one big table support_chat with more than 5 million rows. I need to scan this all the time (3s with ajax) to check new messages on support.  If I move this table to another database in the same computer, can it help anything? (let users, sells, comments table faster)  For example:  db1  users table sells table comments table support_chat table // move this table to db2   db2  support_chat table   They want to keep old things due legal reasons, to have a user support history. The Definitive C++ Book Guide and List How long was Luke Skywalker's training with Yoda? How should we handle a question which was deleted and reasked? A user has asked  which did not receive much attention, and thus the user deleted the post. After some time, the user asked the  (with just slight changes to the title and a tag change), so that it could receive a bit more attention. The strange thing is that the question was not downvoted or poorly written, and yet the user deleted the original post. Now, since the original question was deleted, I could not mark the new one as a duplicate (it threw an error). My question is, how do we handle such questions? Just let them be as such or let the user know about it or is there another way to handle such situations? This is my first post on this forum :)  I've been trying for a while to solve this problem about symmetric difference of two sets:     Given two sets $A$ and $B$, we call symmetric difference of $A$ and $B$ the following:      $$A\mathrel{\triangle}B = (A\cup B)-(A\cap B)$$      Show that if $A\mathrel{\triangle} B = \emptyset$, then $(A\subset B) \vee (B\subset A)$.   I don’t know where to start; thank you very much for the help :) If I design a PC for use as an NPC, how much XP should he give when killed? As part of an early quest, my PCs are likely to face off against a wizard.  The problem here is that the stat block for Mage NPCs listed in the Basic Rules has a Challenge Rating of 6, while the PCs are going to be five Level 1s. So, instead of messing with the stat block and risk weakening it too much/too little, I'm choosing to create a Level 1 Wizard PC and use it as an NPC for this quest.  The problem with that is that, as far as I can tell, there aren't any designated rules for assigning either Challenge Ratings or XP values to a PC. So, should I just give the wizard a Challenge Rating equal to his level (and thus have him give 200 xp when killed), or is there a better way to do this?  (This is different from , because he's asking for a way to assign a level to an NPC, while I'm asking for a way to assign an XP value/Challenge Rating to a PC (for use as an NPC). Similar questions, but different.) Namespaces and Operator Overloading in C++ When authoring a library in a particular namespace, it's often convenient to provide overloaded operators for the classes in that namespace.  It seems (at least with g++) that the overloaded operators can be implemented either in the library's namespace:  namespace Lib { class A { };  A operator+(const A&amp;, const A&amp;); } // namespace Lib   or the global namespace  namespace Lib { class A { }; } // namespace Lib  Lib::A operator+(const Lib::A&amp;, const Lib::A&amp;);   From my testing, they both seem to work fine.  Is there any practical difference between these two options?  Is either approach better? "Basis extension theorem" for local smooth vector fields I am afraid that listing doesn't support javascript.  \begin{lstlisting}[language=javascript] ... \end{lstlisting}   What am I doing wrong? Cannot change lock screen background on Ubuntu 18.04 Before you mark the question as a duplicate, I read all of the posts regarding this, but nothing helped me. I'd like to change the background picture of the lock screen.    I changed the ubuntu.css and gdm3.css accordingly to   #lockDialogGroup {   background: #000000 url(file:///usr/share/wallpapers/minimalistic-gray_00323985.jpg);   background-repeat: no-repeat;   background-size: cover;   background-position: center; }   Which results in a change of the Background of the log in screen, not the lock screen. When I press super + L the screen containing time has the correct background. When I swipe it up to tipe in my password, the purple Ubuntu screen still appears. If I click to change the user, the log in screen appears with the right background. I have the same background picture enabled in gnome tweaks for desktop background and lock screen.   I'm running Ubuntu 18.04 GNOME on a TuXedo Laptop. And I use Communitheme - maybe thats the problem?  Any ideas why it doesn't work? (I rebooted multiple times, so that's not the problem.)  EDIT: The output of sudo nano /usr/share/gnome-shell/modes/ubuntu.json is  {     "parentMode": "user",     "stylesheetName": "ubuntu.css",     "enabledExtensions": ["ubuntu-dock@ubuntu.com", "ubuntu-appindicators@ubuntu.com"] } How do I reset my main keychain and completely delete the old one? I changed my password and its been coming up with all of these popups asking for my new password when I first login. If anyone can help with updating my keychain I would appreciate it or you can just help me completely delete and reset it. Add a time limit before you can vote on a post Help! My master database is corrupt, I can't even bring the SQL instance online! What are my options to get my server back up?   I do have a backup of master, but the  asks me to start the instance in single-user mode, which I can't do!  (Note: I'm leaving this question unspecified as to SQL version, so as to be a more widely-applicable reference. There are some similar questions on DBA.SE, but none that involve the server unable to start.) I have a web page that includes a bunch of images. Sometimes the image isn't available, so a broken image is displayed in the client's browser.  How do I use jQuery to get the set of images, filter it to broken images then replace the src?    --I thought it would be easier to do this with jQuery, but it turned out much easier to just use a pure JavaScript solution, that is, the one provided by Prestaul.