3:12 AM
Somebody made a suggestion for the tag-wiki and the tag-excerpt for on meta. However, the phrasing seems to be more suitable for the tag on the main.
What precisely is the purpose of the tag on meta? For big lists (like list of comment templates)? Or for discussing questions on main which ask for big lists? Or both?

3 hours later…
6:01 AM
The tags , and have been created recently.
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Is there a bijection from $A = ]0,1[$ to $B = A \cup \{1,2,3,4\}$? If there is, give example. I had this question on exam few days ago, and I have been googling for days, but I can't find a solution. I think (probably wrong) that there is not because $A$ is subset of $B$, but I am totally u...

-1

Related to the question Proof that Laplacian is surjective $\mathcal{P}^n\to\mathcal{P}^{n-2}$, in the only answer of this question, @uncookedfalcon explain that, by the inductive hypothesis, the second term of $$x^{M-1} y^- z^- = \Delta(x^{M+1} y^- z^-) - x^{M+1}\Delta(y^- z^-)$$ lies in the im...

4

The question in my homework is: How many functions from $\{0,1\} \times \{0,1\}$ to $\{0,1,2\}$ are there? How many are one-to-one? How many are onto? My first step was to take the Cartesian Product of $\{0,1\} \times \{0,1\}$ in order to get a set $$A = \{(0,0),(0,1),(1,0),(1,1)\}$$ How...

There is also tag-excerpt and tag-wiki for surjectivity.
And tag-excerpt and tag-wiki for injectivity.
What to do with these new tags? I guess they might be useful.
So far the questions about these topics were typically tagged and .

2 hours later…
7:36 AM
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The tags bijectivity, injectivity and surjectivity have been created not so long ago (they are still in the list of new tags.) A natural question is what to do with these tags. So far the questions about these topics were typically tagged functions and/or elementary-set-theory. Considering tha...

I don't see how any of these three tags help, other than causing new users who have no idea how to tag their questions use them instead of proper tagging. But unlike the case where someone uses [real-analysis] or something like that, nobody really follows these new tags, so nobody really notices the questions and tags them appropriately. — Asaf Karagila 32 mins ago

3 hours later…
10:08 AM
I should probably add that I removed similar tags in the past (if my memory serves me right, those were "bi-/in-/sur-jection" named, but who can remember these things?) and I would have removed them judiciously if I had noticed them before you made this post. The real question, now, is whether or not anyone else is going to weigh in. — Asaf Karagila 21 mins ago
@AsafKaragila If we want to see whether somebody else will comment or at least vote, we should wait at least for a few days. (Not everybody reacts within hours of posting.) But I certainly agree that tag-related posts often do not get enough feedback and if they do, the tags can grow in the meantime. If you want to remove these tags preemptively before they become large and removing them would cause bumping many posts, I will not object to it. As list of all taged questions and tag-wikis are saved in chat, it would be relatively easy to recreate the tags (if that is community consensus). — Martin Sleziak 4 mins ago
I guess we can wait a couple of days, at least after the weekend, before concluding that nobody else cares enough to weigh in. :-) — Asaf Karagila 2 mins ago
Re: but who can remember these things? In cases which are not clear cut, I tend to either ask on meta or mention the tag here in chat. So the tags which were removed can sometimes be found here in chat - if they were discussed here.
And sometimes I mention here in chat even tags where it seems clear to me that they should be removed. Mentioning newly created tags might remind some users who care about tagging to have a look at the list of new tags at least occasionally: math.stackexchange.com/tags?tab=new
As I have mentioned that tags might grow before post on meta has enough upvotes to become a consensus, is IMHO a good example. The post suggesting the removal of the tag has 7 upvotes and no downvotes.
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What on Earth is the tag algebraic-identities for? It seems to me that questions containing at least one equal sign get randomly tagged with it, including questions that have nothing to do with algebra. The tag excerpt (there's no tag wiki) mentions "algebraic structures", which I guess includes ...

But the tag grew to more to 200 questions, so it will take some time to remove it. (In fact, I am not sure whether somebody even started with removal of this tag.)
Perhaps could be another example:
Huh, so in the first few weeks, when there were 7 questions tagged functions, there were already no compelling reason to keep that tag. And somehow it is still alive? Amazing. I had assumed it was a holdover from the "olden" days. But it seems I am not quite correct. — Willie Wong Dec 9 '11 at 14:11
Although I think that might be a useful tag if the scope is clearly defined. A long time ago I made some suggestions here.
BTW what would you think about synonyms for this tag with (functions) as the master tag? (And I have made a few comments which are vaguely related to this discussion in tagging chat room,) — Martin Sleziak 19 secs ago
I will mention that since I am travelling, my internet connection is less than ideal. But in case I cannot respond immediately, I will try to do so later. (At least if some response is needed.)
That is an option. Although truth be told, I'm not a huge fan of the functions tag in general. — Asaf Karagila 24 secs ago

3 hours later…
1:37 PM
I have removed tag from the three questions having this tag: 1, 2, 3. However, this is not the first time this tag was created. If it reappears again, perhaps we should start a discussion on meta and try to reach some consensus.