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I am fairly new to Stack Exchange, starting with stackoverflow.com. I added a math.stackexchange.com account to ask questions about my current self-study in Categorical Type Theory. Today, I posted a textbook exercise along with my solutions ((here and here). Some of the comments I have recieved are not quite as positive as I expected. So now I would like to ask the opinions from other members of this community. How do you feel about posting exercise solutions?

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    $\begingroup$ I guess I'm slightly surprised at the response, although I think people were pretty nice in their disagreement. We've had people run down lists of problems that they were doing in the past to a fair amount of approval. $\endgroup$
    – Dylan Moreland
    Jul 23, 2012 at 21:18
  • $\begingroup$ On the other hand, there does have to be some limit on questions like this, which you seem to be in no danger of hitting. But I would suggest that you post problems about which you are somewhat unsure or which seemed particularly difficult/interesting. There are other ways of keeping track of your work, if that's all you want to do. $\endgroup$
    – Dylan Moreland
    Jul 23, 2012 at 21:20
  • $\begingroup$ If you want to keep a record of your work (as you say in the comments), why don't you just make a pdf and store it on your computer? Or, if you want an online record, create a blog? $\endgroup$
    – wildildildlife
    Jul 25, 2012 at 11:55
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    $\begingroup$ Related question at meta.SO: Posting and answering questions you have already found the answer to. $\endgroup$
    – Martin Sleziak
    Jul 25, 2012 at 15:14

3 Answers 3

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I think how you should post the exercise and solution, and how well they are received by the community, might depend on what your ultimate goal is in posting them here. As you haven't said what that is, I'll make a few different guesses and post my opinion on each.

  1. If you want people to check your work, I think it is best if you try to narrow it down to a small area where you are particularly unsure that what you have done is valid. That way, you can ask a more focused question. It's not much fun to check someone else's potentially long and complicated proof for errors that may or may not exist. As your handle is @Code-Guru, consider whether you would enjoy debugging a bunch of someone else's code if they didn't point to a specific block and say, "hey, this is the part which I don't know if it works correctly."

  2. If you want to see alternative solutions, it would be good to say so in the question. Sometimes, askers want help with a specific approach, and posting a completely different solution is not that helpful. Sometimes, answerers see that a solution has already posted, and are discouraged from posting another one. If you do want to see lots of different solutions, it would be good to explicitly ask for them.

  3. If you want to document a result for future reference, StackExchange policy explicitly allows it, but I would suggest that you reserve it for things that could be particularly notable or useful to others. The main reason I say this is because I would not like to see this site turn into a database of solutions to textbook exercises.

In any case, if you just post a textbook exercise and its solution without any context indicating where you're coming from, it's hard for me to tell what you want from us! We're here to answer your questions, but there is no question mark in your question, only an imperative -- and that has already been fulfilled by you. So what do you want us to do?

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    $\begingroup$ My reasons include all the above. The last one currently has the most weight for me, I think. Also I want to share what I have learned with others, which is probably one aspect of "documenting for future reference." $\endgroup$
    – Code-Guru
    Jul 24, 2012 at 23:54
  • $\begingroup$ "more effort to check someone else's proof than to come up with one yourself." Surely this is not a universal truth, even if the universe is restricted to textbook exercises. $\endgroup$
    – Gerry Myerson
    Jul 25, 2012 at 0:35
  • $\begingroup$ @Gerry: I guess you're right. I was thinking of the case when one is familiar with the subject matter and can easily come up with the proof of an exercise; when checking someone else's proof, one has to instead attempt to put oneself in the mind of the other person and discern whether their train of thought is going in the right direction. $\endgroup$
    – user856
    Jul 25, 2012 at 0:58
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    $\begingroup$ @Code-Guru: In that case, I feel that your intentions are overly vague. It sounds like all you're saying is, "Here is a proof. Discuss." Obviously others may differ, but I for one am inclined to ignore such questions (because I see no actual question in them). $\endgroup$
    – user856
    Jul 25, 2012 at 1:16
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    $\begingroup$ @RahulNarain Dear Rahul Narain, "The main reason I say this is because I would not like to see this site turn into a database of solutions to textbook exercises." May I ask the reason? Regards, $\endgroup$
    – Makoto Kato
    Jul 30, 2012 at 1:25
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    $\begingroup$ @Makoto: Because there are so many textbooks and so many exercises that they would down out all other questions on this site. $\endgroup$
    – user856
    Jul 30, 2012 at 2:41
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    $\begingroup$ Did I say down? I meant drown. $\endgroup$
    – user856
    Jul 30, 2012 at 6:25
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    $\begingroup$ @RahulNaran I don't see why it should be frowned upon to provide a good answer to a good question just because it is a texbook exercise. $\endgroup$
    – Makoto Kato
    Aug 7, 2012 at 7:59
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It's allowed to ask a question and answering it. However, it seems that your posted the answer just after the question, and the other members have not time enough to think about the problem. They could avoid reading the answer, but often when we see the question we also see the answer. If you post the answer, I we are not encouraged to think more about the problem, at least less than a question which haven't receive any comment or answer.

In this particular case, it seems that you had the answer before posting the question. I guess the aim in asking the question is to see different solutions. What you can do is post the exercise, then wait a while (say for example 24 hours, in order to allow every body to see the question) and post the answer.

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    $\begingroup$ I would feel somewhat annoyed if I thought I was helping someone solve a problem, only to find out that OP had a solution the whole time. I suggest that if you take this path then you indicate in the question that you have an answer and you plan to post it after some specified interval. But maybe seeing different solutions was not the goal? $\endgroup$
    – Gerry Myerson
    Jul 23, 2012 at 23:40
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    $\begingroup$ It's expressly allowed, even encouraged, to post an answer simultaneous with the question, and that's why the ask-a-question form has an option on it for posting an answer simultaneously. $\endgroup$
    – MJD
    Jul 24, 2012 at 0:23
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    $\begingroup$ @GerryMyerson You are helping other members by providing a good answer. $\endgroup$
    – Makoto Kato
    Aug 7, 2012 at 2:23
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I think it is perfectly fine. I have done it many times with good results. I might should say that when I post a solution, the solution is usually wrong and I know it. I typically post the book's answer.

When I post my answer, I post it as part of the question.

Bob

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