That is, I asked before to check the correctness of my proof of that statement, and the correctness has been confirmed. Could I now flag a question asking for the proof of it as "possible duplicate" of my question?
Could I flag a possible duplicate to a question asking for a proof when I had already asked about the correctness of mine?
$\begingroup$ Which question appeared for first, your proof-checking question or the proof-hunting question? $\endgroup$– Jack D'AurizioApr 4, 2018 at 5:54
$\begingroup$ @JackD'Aurizio: My proof-checking. Maybe I know what you meant, it's about time precedence? But wouldn't it be strange to provide a question as an answer? $\endgroup$– linear_combinatori_probabiApr 4, 2018 at 6:25
1$\begingroup$ Because it would be "This question already has a answer" to "This question already has a ... question". $\endgroup$– linear_combinatori_probabiApr 4, 2018 at 6:27
$\begingroup$ Some past discussions about this topic: Closing as a duplicate if the post contains OP's own proof/solution (and perhaps some of the questions linked there) and Proof-verification and duplicates. $\endgroup$– Martin SleziakApr 4, 2018 at 11:49
If your proof is the natural and generally accepted way to prove a certain statement, and it's hard to come up with alternative proofs, I'd say that's it's safe to close it as a duplicate.
If this is not the case, e.g. when your questions is asking to verify a proof that there are an infinite number of primes, it's certainly not appropriate to close it as a duplicate.