@MartinSleziak Since I already asked it that way, and I doubt there will be more informative answers, I guess we can leave it like that. But you are right: my ignorance made me think that the two maybe related, when they are in fact not.
@WillieWong Thanks for the reply. And I definitely would not call it ignorance. My first impression was similar to yours - that everything will probably be merged under same tag.
I am not sure about that anymore, not even in the case of (approximation), as I explained in my comment.
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BTW WillieWong I see you're dealing with new tags, too; you have removed high-school which was introduced here.
From the newly introducted tags, group-actions seems to be reasonable (in my opinion).
Ok, now as I see your recent edit, you probably don't think that group-actions should have their own tag.
@MartinSleziak you are right. I read that question too quickly. I thought it was about the group operation of the topology group itself, but on second reading it was about G's action on another topological space. So I just reverted the edit. (The tag itself is reasonable; I just mistakenly thought it was misapplied.)
Since we already had plenty of questions about group actions, I have no doubt that the tag will be populated by new questions.
@WillieWong I wasn't sure about the purpose of that tag.
I saw that J.M. made a revision to that question, so I did nothing about the tag. (I thought he saw the tag and decided to keep it.) But maybe he did not notice that tag.
Or maybe he wasn't sure whether to keep or remove - just as me.
@MartinSleziak A long time ago we had a high school tag for tagging questions of "high school level" , it led to some fiery discussions on meta about why such a tag is bad. (Discouraging users etc.) In this case the tag is used differently, seemingly to indicate the rather arbitrary distinction of an age group (14 - 18?). I can't see why such a tag would be useful.
I think the OP just tagged high-school because there aren't really any good tags for the question. And I think that there aren't any good tags because it is not a good question for this site. (Just my opinion.)