MathOverflow's primary goal is for users to ask and answer research level math questions, the sorts of questions you come across when you're writing or reading articles or graduate level books. Of course, individual questions don't have to be worthy of an article, and they don't have to be about new mathematics. A typical example is, "Can this hypothesis in that theorem be relaxed in this way?"

The site works best for well-defined questions: math questions that actually have a specific answer. You'll notice that there is the occasional question making a list of something, asking about the workings of the mathematical community, or something else which isn't really a math question. Such questions can be helpful to the community, but it is extremely tricky to ask them in a way that produces a useful response. So if you're new to the site, we suggest you stick to asking precise math questions until you learn about the quirks of the community and the strengths of the medium. If you have a very broad question (like "Please explain topic X"), try searching Google, Wikipedia, nLab, or looking for survey articles on the arXiv.

Please look around to see if your question has already been asked (and maybe even answered!). If you do post a question that was asked here before, don't worry; somebody will give you a link and close your question as duplicate.

The best way to get great answers to your question is to write a great question. To help you do that, we've written down some guidelines on How to ask a good MathOverflow question.

There are several broad categories of questions that should not be asked on MathOverflow. If a question is closed, it's probably because it fell into one of these categories. If your question is closed, please don't take this to mean that you are not welcome on the site, or think that this will be held against you in the future. A lot of active users have had questions closed at one point or another.

• MathOverflow is not for homework help. Try to make sure your question is of interest to at least one other mathematician. Though there are no hard and fast rules about who may post here, the intended audience is professional mathematicians, mathematics graduate students, and advanced undergraduates. If your question is closed as "off topic," it might be because it was too elementary. This doesn't mean that your question is "bad," just that MathOverflow isn't the right place for it. But there are lots of other math Q&A sites where your question might fit right in, like math.stackexchange.com, Ask Dr. Math, Art of Problem Solving, Physics Forums, or NRICH. If your question was closed as "too localized," it was probably an explicit homework problem (or looked like one). MathOverflow is not the right place for such questions; they send the message that you want somebody else to do your work for you, and you're not even willing to ask it in a general form.
• MathOverflow is not a discussion forum. As a side-effect of being very good for to-the-point questions and answers, the Stack Exchange software is bad for disscusions and designed to minimize them. There's a place for discussion about mathematics, but it isn't MathOverflow. Blogs and threaded discussion forums are a more appropriate place for discussions. For more information on this, see the relevant meta.mathoverflow.net threads (e.g. this one).

• MathOverflow is not an encyclopedia. MO is a site for questions that have answers. MathOverflow visitors should know how to learn new things and do mathematics on their own, but we all get stuck sometimes, and this is where MO saves the day. When you're stuck, you can come to MathOverflow and say "I'm trying to do X. How can I do that? Does this work? Does anybody have a reference?" The idea being that for an expert, it should take very little effort to understand your confusion and set you on the right path. Or maybe a non-expert has come across the same sticking point and can explain how she resolved it. MathOverflow is not the appropriate place to ask somebody to write an expository article for you. If you want somebody to write an article about some subject, you should make a stub on Wikipedia, make a query block on nLab, or make a request on PlanetMath.

• MathOverflow is not for questions about MathOverflow. Mathematicians don't come here to learn about the intricacies of this site; they come here to get answers to their questions. Let's try to help them out by not cluttering up the system with navelgazing meta-discussion. If you want to report a bug, suggest a feature, or discuss the dynamics of MathOverflow, visit our meta-discussion forum, meta.mathoverflow.net. If you're just really interested in how the underlying Stack Exchange software works, consider visiting meta.stackoverflow or meta.stackexchange, but please don't ask MathOverflow-specific there; it will annoy them.

Have a look at the how to ask a good question page. If your question can't be made to follow the guidelines laid out there, it's likely not a very good question for this site.

MathOverflow is not the right place to ask open problems. You should post questions you're actually seriously thinking about. If you're thinking about a well-known open problem, provide some background and ask about something specific related to the problem, like "Such and such is a well-known open problem. So-and-so proposed this and that approach in the 80s. Does anybody know if this aspect of their proposal can be made to work under these circumstances?" If you want to contribute to (or view) a list of open problems, visit the Open Problem Garden.

If it turns out that a problem is equivalent to a known open problem, then the [open-problem] tag is added, and the question is converted to community wiki. After that, the question essentially becomes, "What is known about this problem? What are some possible ways to approach this problem? What are some ways that people have tried to attack it before, and with what results?" That way, the MO thread for the problem becomes a repository of resources related to the problem. Perhaps the answers could be organized by approach, with an outline of the basic approach, followed by a horizontal rule and a summary of what is promising about the approach and why it doesn't give a complete solution.

To join the discussion about how MathOverflow should deal with open problems, go to this meta.MO thread.

MathOverflow doesn't have formal rules about every possible thing that could come up. Roughly, you should think of this site as a large seminar. Be nice. Treat others with the same respect you'd want them to treat you. We're all here to learn together. Be honest. If you see misinformation, vote it down. Insert comments indicating what, specifically, is wrong. Even better—edit and improve the information! Provide stronger, faster, superior answers of your own! Be professional. Doing math with your colleagues is supposed to be fun; that's why you became a mathematician. But just like in a seminar, a certain minimum level of professionalism is expected. If you're unsure about whether something is appropriate, ask yourself, "would I do this in a seminar?"

We also encourage you to use your real name as your username. In your own enlightened self-interest, realise that participating in blogs, MathOverflow, the arXiv, and mathematical publishing are all forms of advertising for your "brand", even if that’s not your principal purpose (and hopefully it’s not). Since job applications require you to write your real name, you might as well use it everywhere else, too.

Using real names reminds everybody that they are corresponding with real people, and it demonstrates a certain level of personal investment in your MathOverflow identity. If you use a pseudonym and you get into some kind of trouble (e.g. fights in comment threads or spammy-looking posts), the moderators are much less likely to give you the benefit of the doubt.

Nope. You can answer and ask questions to your heart's content as an anonymous user, much like Wikipedia. However, there are some things you won't be able to do on the site without registering. But it's easy to register if you want to. All you need is an OpenID account.

If you already have a Google or Yahoo account, then you already have an OpenID. Just click the login link at the top of the page and click the Google (resp. Yahoo) button. You'll be asked for your Google (resp. Yahoo) username and password (this information is never sent to MathOverflow) then you'll be returned to MathOverflow.

If you don't have a Google or Yahoo account (or don't want to use it), you can sign up for an OpenID with myOpenID. After you sign up, you can enter your OpenID at the login screen (your OpenID will look something like http://username.myopenid.com)

Reputation is completely optional. Normal use of MathOverflow — that is, asking and answering questions — does not require any reputation whatsoever.

Remember, MathOverflow is run by you! If you want to help us run the site, you'll need reputation first. Reputation is a (very) rough measurement of how much the MathOverflow community trusts you. Reputation is never given, it is earned by convincing other users that you know what you're talking about.

Here's how it works: if you post a good question or helpful answer, it will be voted up by your peers: you gain 10 reputation points. If you post something that's off topic or incorrect, it will be voted down: you lose 2 reputation points. You can earn up to 200 reputation per day, but no more. (Note that votes for any posts marked "community wiki" do not generate reputation.)

Amass enough reputation points and MathOverflow will allow you to go beyond simply asking and answering questions:

At the high end of this reputation spectrum there is little difference between users with high reputation and moderators. That is very much intentional. We don't run MathOverflow. The community does.

When you make a post, you have the option of making it "community wiki" by checking a box at the bottom right of the input field. This has the following effects:

• You earn no reputation from up/down-votes on that post.
• Users with 100 reputation can edit the post (for non-CW posts, you need 2000 reputation to edit).
• If the post is a question, all answers are automatically made community wiki as well.

There is an ongoing discussion at meta.MO about when a post should be made community wiki. Here are some basic guidelines:

• The most common use of community wiki mode is to ask a question where the goal is to produce a sorted list of answers, rather than a single complete answer. Community wiki mode gets the reputation system out of the way so that people more freely vote up and down to help rearrange the sort order, therby making the page more useful. If you want to ask such a question, please read at least the first two sections of the How To Ask page.
• If you'd like to post a shoot-from-the-hip answer that you'd like other people to flesh out, or if you'd like an answer that pulls together elements from many other answers to make something more complete, you should make a community wiki answer.

There are several ways a question or answer can enter community wiki mode, and most of these ways will occur automatically based on the rules of the system. Posts enter community wiki mode when:

• The body of the post has been edited by four different people.
• The post has been edited eight times by the original owner.
• The post's author checks the community wiki checkbox when composing the question or answer.
• The post is edited by its original author, who when doing so opts to check the community wiki.
• The question generates more than 30 answers. In this case, the question and all answers will enter community mode, as will any future answers.

There is no way to reclaim your post back from community wiki mode. This is to prevent exploits and gaming of the system. Rollbacks do not reverse any of the community wiki mode calculations.

In order to get good answers, you have to put some effort into the question. Edit your question to provide status and progress updates. Document your own continued efforts to answer your question. This will naturally bump your question and get more people interested in it.

If, after two days, you still don't have an answer you like, you can offer a bounty. Slice off a bit of your own hard-earned reputation -- anywhere from 50 to 500 -- and attach it to the question as a bounty. We'll even throw in 50 reputation to sweeten the deal. The bountied question will appear with a special icon in all question lists, and it will also be visible on the home page Featured tab.

Once initiated, the bounty period lasts 7 days. If you mark an accepted answer, your bounty is awarded to the answerer (do note that accepted bounty answers are permanent and cannot be changed). If you do not accept an answer in 7 days, here is what happens at the end of the bounty period:

• The highest voted answer created after the bounty started with at least 2 upvotes will be automatically accepted. Half the bounty will be awarded to the owner of that answer. If there's a tie for highest voted, half the bounty is evenly divided among those owners (I think).
• If there is no answer meeting the above criteria, and you as the question owner have not opted to accept an answer, you forfeit your right to ever accept an answer to your question.

In any case, you will always give up the amount of reputation specified in the bounty, so if you start a bounty, be sure to follow up and accept the best answer!

Of course, bounty awards, like all accepted answers, are immune to the daily reputation cap and community wiki mode. Note: just as you don't earn any reputation for accepting your own answer to a question, you do not get awarded the bounty if you accept your own answer.

Like Wikipedia, this site is collaboratively edited. If you are not comfortable with the idea of your questions and answers being edited by other trusted users, this may not be the site for you.

When you post on MathOverflow, you retain the copyright to your words, but you release them under the Creative Commons Attribution-Share Alike license, the same license used by Wikipedia. This license is permissive, but does require attribution; if you want to republish something from MathOverflow, please read over the attribution requirements. Since the content belongs to MathOverflow's users, we regularly post sanitized copies of the database at dumps.mathoverflow.net.

MathOverflow LaTeX support is , a method of including mathematics in web pages using javascript. We'd like to extend a huge thanks to the MathJax team for developing it.

Basically, anything between dollar signs gets interpreted as mathematics (many LaTeX commands are implemented). For example $f\colon X\to Y$ produces the result $f\colon X\to Y$.

If you want to learn about how to do MathJax ninjitsu (like useing MathML instead of HTML-CSS rendering), right click on some math to get the MathJax context menu.

STIX fonts. MathJax will render math without you having to install anything, but it will work faster if the STIX fonts are installed on your computer. See the MathJax fonts page for instructions.

About the live preview. When you compose a question or answer, you should get a live preview of what your post will look like. If the preview is horribly broken, please report the problem on this meta.MO thread. There's one bug you should know about. The MathJax script gets whatever Markdown spits out, and underscores and asterisks are special Markdown characters, so things between underscores (or asterisks) get converted to italics. Then when the MathJax script looks at the contents of the preview box, it doesn't find any underscores or asterisks, so it gets confused. Workaround: If you put backticks around your math (i.e. type `\$f'_n=g_{n+1}\$`), then Markdown will interpret it as code, so it will leave it alone for MathJax.

Note that curly braces and backslashes are also escapable Markdown characters for some reason. This means that if you type "\{", Markdown will convert it to "{". To get the right input to MathJax, you have to escape the backslash (which would otherwise escape the {) by typing "\\{". You could also simply put backticks around your math, as described above.

Just be really awesome at asking and answering math questions. Supposing you've done that, you can have a look at the Tips and Tricks page. You may also want to learn about how to use the editor to effectively format your posts.

MathOverflow runs on Stack Exchange, the hosted service that provides the same software as the popular programming Q&A site Stack Overflow. The hosting cost is paid from the research funds of our generous benefactor, Ravi Vakil of Stanford University.

Keeping MathOverflow clean, civil, and on topic are its moderators: David Brown, Scott Carnahan, François G. Dorais, Anton Geraschenko, Scott Morrison, and Ben Webster:

You can contact the moderators by emailing moderators@mathoverflow.net. If you have any other problems with the site, contact Anton Geraschenko (geraschenko@mathoverflow.net).

The best way you can help us run the site is to use it. Ask good questions. Give good answers. Vote up good questions/answers and vote down bad questions/answers. As you gain more reputation, you can help in more and more ways, like editing posts to make them clearer and voting to close inappropriate questions.