This can only be done by moderators. At best what I could do as a regular user would be to check whether Google remembers some deleted posts by this user - I only see there the one you have mentioned: Suppose $X=\mathrm{int}(A) \cup \mathrm{int}(B)$, $Z=X\setminus B$, and $B=X \setminus Z$. Why is $X\setminus \mathrm{int}(B)=\mathrm{cl}(Z)$?.

The recent deleted questions in mod tools (available to regular users with 10k reputation) do not show self-deletions.

It would be possible to check deleted posts using SEDE, some queries have been suggested in this answer. However, there I cannot filter the deleted questions by the username.

I could, for example, check recent deletions in the general-topology tag if I suspect that this is the tag this user uses most often. But this would mean to go through the whole list one by one.

In short, I think this is better to leave for moderators, they have tools which they can use to search for such posts.

Now I feel quite stupid that I did not find the above question. It is on the frequent tab of the proof-verification tag on meta. (I have been looking among questions tagged solution-verification. BTW I am not really sure whether it's necessary to keep this as two separate tags on meta.)

@AsafKaragila It has been more than a day or two. :P

@XanderHenderson I said "day or so", not "day or two". :P

Ah. That explains it.

A total reading comprehension fail on my part. I am sorry to bother you. :P

Also, my answer was going to be somewhere along the two answers posted, more leaning towards rschwieb's answer.

I figured as much.

My answer would be to burninate the proof-verification tag. ;)

@XanderHenderson That just deals with the symptom, not the actual problem.

It's like saying "Oh, someone bubonic plague! Let's flay them, so they don't show any more of those nasty pustules..."

I'm not sure that I buy that argument. I think that the proof verification tag gives license to people, in the sense that it makes them think that it is okay to post "grade my homework" style questions. If there were no such tag, it would be easier to say "Hey, that result has already been proved here, here, and here. Dupe hammer."

But my opinion is likely far out of the mainstream, so I try to ignore that tag as much as possible.

@XanderHenderson I can suspend you for a year, this way it will be very easy for you to ignore that tag... :P

But... but... but... :(

@XanderHenderson Only if you want. Or do something very severe.

Heh. No, like I said, I mostly ignore the tag. I don't think it is healthy for the site, but I recognize that I am in the minority in holding that opinion, so I try to close my eyes and look the other way.

At the same time!

I am looking with my eyes closed!

@MartinSleziak sorry it became more early evening then aftenoon. There is no pattern as far as I can tell. But I undeleted and explained that this should not be done. (Tehnically I'll do it in 30 second.)

Thanks!

I pinged stressed out about this - since this inquiry originated from them.

@quid Just to have some future reference, when somebody encounters things like this, one of possible way to proceed is to flag for moderators' attention, right?

And another possibility might be to suggest undeletion - for example in CRUDE - which is exactly what stressed out this in this case.

If a user deletes their question shortly after having received an answer I virtually always undelete and explain that this should not be done. (Exceptions might be made in case a good reason is provided or the thread is really bad.) Thus, flagging is an option and might indeed be the best option. Of course requesting undeletions in the usual way, such as asking in CRUDE, is also a good option.

Inquiring whether a user has a pattern of deleting content is better done in a flag. Generally most anything that concerns a user (as opposed to a post) is better communicated via flags, especially if the context is negative.

^^ @MartinSleziak (I did not ping you in the comment in case you prefer to have a neutral comment to link to.)

Thanks for the response!

And it's good to hear that this instance is not a case of repeated problematic behavior.