Prove that n is a prime number if and only if $(n−2)! \equiv 1 \pmod n$.
Showing a number $n$ is prime if $(n-2)! \equiv 1 \pmod n$
I would like a way to mark a question in the Unanswered "my tags" page as something I'm not interested in or able to answer The /unanswered/tagged?tab=mytags page gives a list of questions from my favorite tags that are currently considered "unanswered" - they have no up voted or accepted answers. I think it's good to put them in front of me easily, but even though they have one or more tags that I'm interested in, I may not have the knowledge, ability, or interest to write an answer to them. However, they will remain on this page until someone writes an answer.  I would like to be able to dismiss questions from views, like this one, that show me interesting questions. I may choose to share them on my social media to get them views and answers, but I don't want to continually see them. Instead, I want to be able to use views like unanswered/tagged?tab=mytags as a queue of things that could use my attention. Can a Paladin take levels of other classes? In 3.5 D&amp;D,  have severe restrictions on multiclassing:     Like a member of any other class, a paladin may be a multiclass character, but multiclass paladins face a special restriction. A paladin who gains a level in any class other than paladin may never again raise her paladin level, though she retains all her paladin abilities.   Because Pathfinder is based on 3.5 D&amp;D, do Pathfinder paladins face the same restriction? That is, if a Paladin multiclasses to say, a fighter, can she take another level of Paladin later on? How do you convert a cake recipe to make brownies? Why is \[ ... \] preferable to $$ ... $$? I've heard that you should use \[ ... \] for displayed equations instead of  $$ ... $$, but why is that?  I'd assumed that it's so that you can more easily tell which are starting and which are ending delimiters, but if I always use a syntax-highlighting text editor, I can see that easily based on the color of the symbols.  Is there any reason for this suggestion? How do I find out command line arguments of a running program? I'm looking for a tool or method to find out what command line parameters have been passed to a program, for example when it was run by another program (launcher-application scenario). I am downloading the HTML source page of a website using cURL command. The problem is, I do not want most of the contents in the page. I just need the first 100 lines of the source page. Is there a way to stop the download of the page after first few lines?  Currently, I have the below command working but it does not seem to be time effective.   curl -r[0-1] "http://www.freebase.com/m/045c7b" &gt; foo.txt   I tried changing the value from 1 to .5 and .05 and still the entire web page is getting downloaded.   I am looking at time less than a second to execute the above command.    EDIT  From the man page of cURL, I see that "You should also be aware that many HTTP/1.1 servers do not have this feature enabled, so that when you attempt to get a range, you'll instead get the whole document." So if the server is not supporting the range querying, is there some other command in nix environment which will help me accomplishing what am trying to do? Who are the diamond moderators, and what is their role? Some people have a diamond after their username (e.g. )    What special privileges do diamond moderators have? How can I become a diamond moderator? Who are the diamond moderators?  How many are there?      For more information, see  in the .     Note: not to confuse with certain Stack Exchange employees, for example  members or "community managers", who often have diamonds as well, but are not ordinary moderators. Elements of order 2 in $D_{2n}$ Im new at this abstract algebra stuff and im not comfortable with the proofs techniques yet, so I have a question related to the elements of order $2$ in $D_{2n}$.  Problem:   Prove that $\{x\in D_{2n}|x^{2}=1\}$ is not a subgroup of $D_{2n}$ for $n\geq 3$.   By now, I know that all the elements of the form $sr^{k}$ has order $2$ because I tested by brute force haha, but my real question is how do I prove prove that. How do I have to proceed to prove that $sr^k$ has order 2.  Any help will be really appreciated, thanks so much &lt;3 Why do we need Diffie Hellman? Diffie–Hellman offers secure key exchange only if sides are authenticated. For authentication, sides are using public/private key. So if side A knows the public key of the side B, then A can simply use that key to encrypt the message (or the new session key).  Why bother to use separate key exchange algorithm? Can 12 teams in 6 disciplines play 6 rounds without repetition? Should I use single or double colon notation for pseudo-elements? Unsure whether to use "enquire" or "inquire" Evaluate $\lim_{n\to \infty} \sum_{r=1}^n \frac {1}{2^r}\tan \left(\frac {1}{2^r}\right)$ Evaluate $$\lim_{n\to \infty} \sum_{r=1}^n \frac {1}{2^r}\tan \left(\frac {1}{2^r}\right)$$   I tried to create a telescoping sum but I couldn't. The last step I could reach was turning the limit into $$\lim_{n\to \infty} \sum_{r=1}^n \left(\frac {1}{2^r(1-\tan (2^{-r+1})} -\frac {1}{2^r(1+\tan (2^{-r+1})}\right) $$  But couldn't proceed further. Also I thought about Riemann sums but it was a pure dead end.  Any help would be greatly appreciated Solving $(z+1)^5 = z^5$ What it says on the tin, a foreign friend of mine has asked and I can't tell him; apart from it sounding horrible.  For example:  "Why is it raining today?"   Instead of:  "Why it is raining today?" Take a look at this example schematic:  The chip in question is the  and as you can see power is provided on both sides (with a 100nF cap to smooth noise I guess). Is this strictly required or could you put power into one side and just ignore the other? I know that I have just put power in one side and everything still seems to work fine but I feel uneasy with doing that. I feel that they would not waste pins that could be doing something useful by having an extra pair of power in/out pins. For what purpose does this PIC MCU (and others like it) have multiple power pins? How do you challenge the closing of one of your questions? As a newcomer to StackOverflow, I recently asked my first . I wanted to start with a fairly safe general question, to get the feel for how the site worked. My question was intended to be programming-related, but my original wording was not clear enough, so another user decided to close it.  I've re-phrased my question, and had received one useful answer before the question was closed, but I'm not sure what the procedure is after your question is closed to allow people to post answers again...  I've checked the FAQ and About pages, searched the SO questions, but have had no luck. Could someone point me in the right direction as to how I get my question re-opened, or if it is possible to do at all? Where to place 'only' relative to prepositions? I know that questions about the placement of 'only', are often asked here; accordingly, I searched for an answer to my question before posting it.  Question  Where are focusing adverbs placed relative to prepositions?  For example,   For his presentation, he needed to talk only about tomatoes. For his presentation, he needed to talk about only tomatoes.   My Attempt to Answer the Question  In both examples, it seems to me that 'only' is placed close enough to what it is intended to modify (the topic of the subject's discourse: tomatoes) that I cannot see any justifiable misinterpretations.  One of the examples sounds better to me, but at this point in my studies, I am more interested in what the traditional rules of grammar require, than in how the wordings sound. Finding an uncountable chain of subsets the integers How to find an uncountable subset of $P(\mathbb{N})$ such that every two elements of it can be compared. In fact, give an uncountable subset of $P(\mathbb{N})$ such that has totality property. We mean by $P(\mathbb{N})$, the powerset of natural numbers set $\mathbb{N}$. Can you choose which version of a game to play on Steam?