Posting a solution from elsewhere and asking whether it's correct

Question

I have seen postings on math.stackexchange starting "I found this solution somewhere on the internet to [problem x.y in textbook]" (often without information about where they found it, just a quote). The post might continue in one of these ways:

1. Is it correct?
2. Why did they use this approach?
3. I think these are mistakes. What about these points later on?

Type 1: are they really expecting math.stackexchange users to proofread some random solution that they found? (I don't think this is the same as a typical proof-verification post, since those should be asking about poster's own work.) Type 2: are they expecting users to psychoanalyze the original author? I suppose not, but if they're basically asking, "How do you come up with an idea for how to solve this problem," then that feels like too open-ended a question. Type 3: if they've already found several clear mistakes, why are they putting any faith into the rest of the purported solution?

Are these appropriate types of posts? What are good ways to respond to them while being polite and respectful? Type 2 in particular seems like the sort of question that could be refined and turned into something of higher quality with the right sort of feedback, but I don't know what that feedback should be.

Or do I just try to ignore this type of post and let someone else deal with it?

Answer 1

TLDR: just ignore them if they don't interest you but are otherwise high quality.

If theres too many then maybe we should curtail these but in general when I see a "check my work" question my gut reaction is "I'm not interested but maybe someone else is" so I'll avoid closing/downvoting if the question reproduces all of its results without requiring you to click on links outside of stackexchange, has proper LaTeX, and seems to contain a good faith effort of the author to point out which parts of the proof they are not sure about.

Answer 2

If you think the question is unlikely to be useful to others in the future, downvote. Or, do nothing.

Then, move on with your life.

Don't vote to close (unless it falls into the existing categories for closing). In my opinion, "please check this solution" questions often are not very high quality, and rarely contribute much to our mission to create an archive of knowledge. In such cases, those are two good reasons to downvote. However, they are not valid reasons to close the question.

I also suggest you distinguish "is this solution correct?" from "is the step in line 7 valid? I have the following doubt: ..." I think the latter questions are better. I personally will often downvote the former but often upvote the latter.