I just commented the solution to a question that was obviously not research level. Then I deleted the solution again since providing it might encourage people to again asking such questions.

Nevertheless, it happened regularly (if I remember right) that I have seen people giving solutions, so my question is:

Is it suitable to provide solutions to well stated questions that are obviously not research level.


The answer is no, it is not a good idea to hand out answers to trivial problems, but that doesn't mean we won't do it. Many MathOverflow users find it very difficult to resist the urge to write a solution to a problem. This is actually one of the root causes for MathOverflow's success: Mathematicians love solving problems and, to fully savor it, a solution must be posted somewhere... like MathOverflow!

This source of MathOverflow's success is also a source of problems, like the one you point out. Various etiquette rules regarding problem solving have similar consequences, such as the silly rule that only the first solution counts. So the answer to your question and a lot of related questions is always the same: it might be preferable not to do this or that, but it would be equally detrimental to enforce a rule saying not to do this or that. This is why MathOverflow historically has only one rule: you must wear pants!

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    $\begingroup$ We don't enforce a rule not to do it. But we can (and do) downvote those who do it. To be really mean, we can downvote and not comment explaining why the downvote! $\endgroup$ – Gerald Edgar Dec 26 '13 at 14:54
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    $\begingroup$ For new users it might be best to just leave a comment since they might not know not to answer. $\endgroup$ – Benjamin Steinberg Dec 26 '13 at 18:51
  • $\begingroup$ If a question is migrated e.g. to Math.SE, existing answers are deleted. -- Maybe this could be done in all cases when a question is closed as "off-topic"? -- This might reduce the number of answers squeezed in immediately before a question gets closed. $\endgroup$ – Stefan Kohl Dec 26 '13 at 23:19
  • $\begingroup$ I don't know whether it's often to migrate questions between MSE and MO. In the past, it's impossible for the difference of the versions of stackexchange. $\endgroup$ – Yai0Phah Dec 28 '13 at 14:38
  • $\begingroup$ It is sometimes possible that an open question is really hard and received no solution in MSE, therefore one has authority to require operators to migrate, and conversely, operators could migrate off-topic questions from MO to MSE. $\endgroup$ – Yai0Phah Dec 28 '13 at 14:40

It is perfectly acceptable to answer non-research level questions in comments if you feel like doing it. What is trivial to an expert is often hard for anyone else. I wouldn't send a colleague who knocks on my door with a trivial question to go take a graduate course. We of course should firmly discourage users who flood MO with trivial questions.

Clarification in response to comments by quid and Niemi:

  1. The definition of a "research level question" (recalled in comments) is very inclusive, and pretty much any question asked by a professional mathematician in the process of his/her work will be research level regardless of how trivial it is. I like it that way. I see a trend to on MO to agressively close trivial questions, and I see that many users do not even want us to answer such questions. The latter is (in my view) harmful to the MO as it makes the site less welcoming, and frankly less useful to my own work.

  2. As to whether one should respond to trivial questions in a comment or in a formal answer, I do not really care. My preference is to respond in comments because I find distasteful to earn reputation points on such answers, but then I also find the whole reputation point system somewhat silly--it ought not be a motivation for answering questions. What is essential is that those trivial questions get answered. If they don't, we are telling our colleagues that they are not welcome, and this is self-destructive for the MO.

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    $\begingroup$ But then, I assume you would also not say about yourself that the purpose of your existence is for discussing research level mathematics. $\endgroup$ – Niemi Dec 30 '13 at 19:00
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    $\begingroup$ I answered things in comments sometimes, too. Yet I think it should really be an exception or have a clear point. Say, if somebody were to comment: "This is off-topic, just note [some terse answer/hint] If you need details ask on math.SE." I could consider this as alright. Yet if somebody just answers in a comment (instead of an answer) without clear explanation why they do so, this causes issues, and in particular raises the question why only a comment. I think there is some danger in having some middle-ground of comment-answer. (semi-OT I did not even read OP as asking about comm ans) $\endgroup$ – user9072 Dec 30 '13 at 23:01
  • $\begingroup$ @Niemi: sorry I do not understand your comment. $\endgroup$ – Igor Belegradek Dec 30 '13 at 23:05
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    $\begingroup$ I strongly assume @Niemi's comment is motivated by the fact that the expressed purpose for the existence of the site MO is research-level questions. By contrast the users of this site (presumably) do not have such a declaration attached to them (or on their door). $\endgroup$ – user9072 Dec 30 '13 at 23:10
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    $\begingroup$ Let me quote: "MO'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". By this definition all questions I asked on this site are research level. In retrospect some of them turned out to be trivial (i.e. a suitable expert could answer them without thinking). If we discourage trivial research level questions, the MO will become less attractive to me (and I suspect to many others). $\endgroup$ – Igor Belegradek Dec 30 '13 at 23:48
  • $\begingroup$ I am not sure what we are discussing now. If the question meets the criteria for on-topic it should be answered, via an answer and not only a comment. What is the point in not using an answer but a comment in stead? I do not know which (type of) question OP had in mind exactly. But Christian Stump wrote "obviously not research level" (my emph) which to me does not include questions that came up in a research context (with that context being mentioned) that turn out to be easy. $\endgroup$ – user9072 Dec 30 '13 at 23:58
  • $\begingroup$ @Igor Yes, quid is right. I wanted to stress the difference between questions that I would personally answer and questions that might better be not answered here. If a colleague asked me why the neutral element of a group is unique, I would be rather surprised, but I would of course answer him. I would, however, not expect this kind of question to be answered on this site. $\endgroup$ – Niemi Dec 31 '13 at 0:45
  • $\begingroup$ Could you please clarify what is the meaning of 'in comments' in your answer. BTW, answering only via a comments is also (in some people's opinion at least) a way of being discouraging towards a question. To me it thus seems your position is self-contradictory (except if your goal is to make MO less attractive for yourself). $\endgroup$ – user9072 Dec 31 '13 at 15:33
  • $\begingroup$ Thanks for the clarification. Your point 1 is a complex subject, let me focus on 2 what I was asking about. On a practical note, if you want to avoid getting points I recommend giving the answer in CW mode instead. But still I find such things worse than not answering. To stay in the real world analogy, I can envision various scenarios were not answering a question can happen without causing bad feelings, while for answering a question in an arrogant/condescending way this is more difficult. Answering in a comment can be perceived (sometimes rightly so) as the latter. $\endgroup$ – user9072 Dec 31 '13 at 18:49
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    $\begingroup$ I am not interested in discussing 2, which I only mentioned for clarification. $\endgroup$ – Igor Belegradek Dec 31 '13 at 19:11
  • $\begingroup$ It is fine if you are not interested in discussing it. However you should take notice that you declared something as "perfectly acceptable" that was criticised by others on various occasions (this is just about the answer or comment distinction, there was a meta thread just about how to deal with the problematic situation the creation of which you declare here as "perfectly acceptable".) Anyway, it is beyond my comprehension how you can consider it as irrelevant to create an unwelcoming atmosphere via answering via comments instead of answers in view of the other things you say. $\endgroup$ – user9072 Dec 31 '13 at 21:01
  • $\begingroup$ @quid: 2 is irrelevant to the original question (by Christian Stump) hence this is no place to discuss it. Closing the question without any answer is much more unwelcoming than answering in in comments. I see how some can find answering in comments condensating, but in my opinion they should get a grip. Condensating answers are common even when you buy someone's expertise (lawyer's, doctor's etc). On MO those who answer DONATE their time and expertise, so as long as the answer in comments is polite, I see no issue. $\endgroup$ – Igor Belegradek Dec 31 '13 at 21:26
  • $\begingroup$ Why did you bring it up in the first place if it is irrelevant?! $\endgroup$ – user9072 Dec 31 '13 at 21:36
  • $\begingroup$ I never meant to stress "in comments" in the answer-this is just how I prefer to answer trivial questions. In retrospect it was a distraction from my main point. $\endgroup$ – Igor Belegradek Dec 31 '13 at 22:29
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    $\begingroup$ I disagree that any question can be research-level just because the stated definition includes questions that show up in your research. Any question that can be answered by all undergraduate students is not of research-level (spirit of the law versus letter of the law and all that). If someone is doing research and in that context asks a trivial question here, then that is ok, but the question should not get more than a passing reference to the triviality as an answer. If a user repeatedly has such questions, then they might want to consider whether research is really their cup of tea. $\endgroup$ – Tobias Kildetoft Jan 1 '14 at 19:32

In general, one should not answer questions that are (in one's opinion) off-topic for the site, which includes mathematical questions that are obviously not research level.

Of course, there is some variance and room for personal judgement here, and one can also make exceptions here and there, but as a default one should not answer such questions.

There are also some users that point out in comments when people answer 'too simple' questions that they should not have answered (some also down-vote in such cases).

A way to proceed, for a question of the type you describe, could be to suggest or vote to migrate to http://math.stackexchange.com (provided the qestion also has some context and the only reason for it not being a good fit here is the level).


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