I just answered a comment of Sean Roberson on this question, and everything has disappeared. All in all:

  • Comment of SR, that a product formulat may help, giving a link to this site.
  • I reply that it's not much simpler as one gets $\dfrac{\cos \frac{x-y}{2}}{\sin \frac{x+y}{2}}$.
  • Reply by SR that it was just a thought.
  • I answered that it was still useful, but everything of the above disappeared in the meantime!

I know it's possible to flag a comment as obsolete, but I'm not sure it's what happened - and it would be very fast to get "obsoleted"!

Is there a way to know for sure what really happened?

  • 3
    $\begingroup$ I can confirm that three comments were deleted. Your hypothesis is correct - they were marked obsolete, and they were removed. Sometimes, the mods are fast. $\endgroup$
    – davidlowryduda Mod
    Commented Oct 26, 2016 at 20:50
  • 1
    $\begingroup$ What does it mean when a comment is "obseleted"? $\endgroup$
    – suomynonA
    Commented Oct 26, 2016 at 23:17
  • 4
    $\begingroup$ @suomynonA: For example, if I comment on a post with "There might be a typo at such and such", and the OP edits it, they could flag it as obsolete; or they can thank me, and I can delete my comment and flag theirs as obsolete. Namely, the comment has been rendered moot by some change in the situation. Of course, some comments have historical value, and are not obsolete even after the fact. $\endgroup$
    – Asaf Karagila Mod
    Commented Oct 26, 2016 at 23:23
  • $\begingroup$ @AsafKaragila Didn't know that; usually I just let comments stay... $\endgroup$
    – suomynonA
    Commented Oct 27, 2016 at 0:29
  • 2
    $\begingroup$ @suomynonA: That's an option. But sometimes you are having a somewhat irrelevant discussion with someone, then you decide to stop. You remove your comments, and then what about his? They now only half of a discussion. So the right thing to do is to flag them as obsolete (or if there are many of them, flag the post itself with the free-form flag and request a comment cleanup on aisle obsolete). $\endgroup$
    – Asaf Karagila Mod
    Commented Oct 27, 2016 at 0:46
  • $\begingroup$ @mixedmath Ok, thank you for the clarification! $\endgroup$ Commented Oct 27, 2016 at 5:53
  • $\begingroup$ @Asaf: I'd be curious to see an example of a comment you consider to have "historical value". (I swear I won't delete it right away! 😉 ) $\endgroup$
    – user642796
    Commented Oct 27, 2016 at 9:52
  • 1
    $\begingroup$ @arjafi: There are discussions that while end up being somewhat irrelevant, did have some impact and some implication on the general things. I don't have a specific example in mind right now. And unfortunately, I don't have much time to spend and search for one. $\endgroup$
    – Asaf Karagila Mod
    Commented Oct 27, 2016 at 10:21
  • 1
    $\begingroup$ @arjafi... You mean you haven 't seen questions where the only answer occurs inside a comment? $\endgroup$
    – GEdgar
    Commented Oct 27, 2016 at 14:15


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