@RicardoAndrade for the PDE thing, generally speaking I would rather leave tags an OP added except they are completely misplaced (or except perhaps I'd need 'space' for a missing one).

@quid: Thanks for the good suggestion.

@RicardoAndrade You are welcome! For the dvisibilyty tag, not sure. On the one hand I like the idea. On the other hand it feels strange and could be unintuitive for people to find it, if say a question on the number of divisors of an integer were tagged divisibiity.

I mean the 'find' rather in the sense of finding the tag, not the question.

To put this differently, for some of the more arithmetic questions tagged divisors I think it would be good. But maybe not for all. But then on second thought there is also the tag arithmetic-functions, so one could use this instead of divisors then.

I think I have to take a closer look to form a final opinion.

Thank you also for the 'spin' reply. Since the question is already a bit out of site, I will leave it now, but keep an eye on the tag.

out of site...sight, of course...since some time I have the habit to type way too "phonetically" and this with a bad accent.

@quid: You make good points. However, the tag 'arithmetic-functions' might be problematic due to having a somewhat counter-intuitive name: perhaps not many people will think of it. Thanks for taking a look at this. please let me know if you come to any other conclusions regarding the tag 'divisors' and its companions.

Regarding the 'spin' tag, it was no problem. I will try to keep tabs on that tag, but these bad tags can have a way of surviving... :)

Perhaps I should have just removed it immediately, which I considered doing...

@RicardoAndrade I will have a closer look at divisors, and think a bit about it. re 'surviving' I was so annoyed (well not that much but still a bit) I did not catch the postdoc tag in time; as the things got migrated they got locked and now we have it (for 30 days).