The following is the tag info for the functions tags:

In mathematics, a function is a relation between a set of inputs and a set of permissible outputs with the property that each input is related to exactly one output. A function is defined by its set of inputs, called the domain; a set containing the set of outputs, and possibly additional elements, as members, called its codomain ; and the set of all input-output pairs, called its graph. Sometimes the codomain is called the function's range, but more commonly the word "range" is used to mean, instead, specifically the set of outputs (also called the image of the function). For example, we could define a function using the rule $f(x) = x^2$ by saying that the domain and codomain are the real numbers, and that the graph consists of all pairs of real numbers $(x, x^2)$.

In 2010 the tags emerged and it is suggested to be deleted. Seems nothing had been done. There were around 500 questions tagged with "functions" in 2011. Now in 2018, we have over 19,000 questions tagged with "functions".

Probably we all know why: whenever a question involves functions, people add the "functions" tag.

Not only that this is not what the tag info suggested, but also it makes the tag useless.

My questions is: How can we discourage people from using the "function" tag?

This is what I have in mind:

  • Add to the tag info that one should not use the tag simply because you used functions in the questions (But really, who will read the tag info before using the tag?)

  • Change the name from function to mapping. (Not sure how it can be done).

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    $\begingroup$ I agree - the functions tag is useless and way too broad. Basically every question could be tagged that. $\endgroup$ – user223391 Feb 5 '18 at 3:47
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    $\begingroup$ Does having it as a tag even contribute anything at all? The only usage I can see other than "this question has a function in it" is when the questuon specifically relates to the function-ness of a function, which may be better served by something like a "well-defined" tag. $\endgroup$ – Alexander Gruber Feb 5 '18 at 5:42
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    $\begingroup$ @AlexanderGruber I have made a suggestion about what should be in the functions tag some time ago: About (functions) tag. Other than one comment, nobody participated in that discussion - and the answer with the proposal got to score +1, which doesn't really count as consensus. $\endgroup$ – Martin Sleziak Feb 5 '18 at 7:27
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    $\begingroup$ To add som specific examples, I would consider the question listed here as reasonable candidates for the (functions) tag: Overview of basic results about images and preimages. Similarly, the typical questions about properties of injective/surjective/bijective functions. $\endgroup$ – Martin Sleziak Feb 5 '18 at 7:29
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    $\begingroup$ There are currently 3294 questions with only the [functions] tag. This is quite an immense effort to retag them and blacklist the tag entirely. $\endgroup$ – Asaf Karagila Feb 5 '18 at 10:36
  • $\begingroup$ @MartinSleziak: The question you linked probably include most of the questions types that should be tagged "functions", if not all. If used correctly I guess there should not be more than 1k such questions, dupicates included. $\endgroup$ – user99914 Feb 5 '18 at 14:43
  • $\begingroup$ @AsafKaragila That's why I hesitated to suggest blacklisting the tag. $\endgroup$ – user99914 Feb 5 '18 at 14:45
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    $\begingroup$ John, in the past with blacklisted the [homework] tag. I don't remember the exact number, but there were a lot of questions which had only that as a tag. After it was clear the consensus was to blacklist, a massive effort was undertaken to fix these questions, and then the blacklist happened. So first we need to discuss, in a certain urgent immediacy, whether or not this tag should be phased out entirely. $\endgroup$ – Asaf Karagila Feb 5 '18 at 14:46
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    $\begingroup$ I am not sure if we will have a majority decision on that. I think it is clear this tag are misused everyday, but some questions could be tagged "functions", as Martin suggested. In the mean time I will try to re-tag/close/delete some questions with that tags slowly. $\endgroup$ – user99914 Feb 5 '18 at 19:03
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    $\begingroup$ This is why I said we first need to poll for more opinions. I flagged for moderator attention to add a [featured] tag to increase visibility. I hope this will be done. $\endgroup$ – Asaf Karagila Feb 5 '18 at 22:08
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    $\begingroup$ While I agree that there is a certain class of questions that could benefit from being tagged [functions], I'm not sure how much benefit there is to this that would not already be gained by tagging them with [elementary-set-theory]. And as long as the [functions] tag exists, it's going to be abused a lot. $\endgroup$ – Eric Wofsey Feb 6 '18 at 0:10
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    $\begingroup$ What about renaming it to "function-properties"? It's certainly more specific than "functions" and probably wouldn't be applied to anything with a function in it. $\endgroup$ – celtschk Feb 6 '18 at 9:03
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    $\begingroup$ I think that some polling answers should be posted, perhaps. It would help to get some actual feedback from the community. So far all we have is a bunch of comments and very little active participation as far as discussions go. $\endgroup$ – Asaf Karagila Feb 12 '18 at 16:13
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    $\begingroup$ 2) I don't think moderators are responsible for that. Moreover, if such a measure is needed, probably stronger measure has to be done on the tag itself. 3) Most of the question wrongly tagged as "functions" are not from "functional analysis". @Narasimham $\endgroup$ – user99914 Feb 25 '18 at 3:11
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    $\begingroup$ The description of the function tag should not just be a definition of "function." The description of a tag should be what the tag is for, not a definition. Doubt that would help solve the problem of misuse of the tag, since most posters don't read the description, I'd guess. $\endgroup$ – Thomas Andrews Feb 28 '18 at 15:55

The name of the "functions" tag should be changed.

We could change it to "mapping", or "functions-properties" as suggested.

Quoting celtschk: It's certainly more specific than "functions" and probably wouldn't be applied to anything with a function in it.

This should also be implemented quite easily. It is not completely clear how effectively it could be though. We might also needs to go back to the existing 19000 questions to see if the new name are suitable for them.

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    $\begingroup$ BTW, my suggestion was "function-properties", not "functions-properties". $\endgroup$ – celtschk Feb 26 '18 at 7:37

We should blacklist the "functions" tag.

Just like what we did for homework. In paricular, this means similarly that we will request the SE team to completely remove the tag from the system and ensure that it cannot be re-created. This will result in a large number (at present over 3200) of untagged questions, which will be the responsibility of the community to fix.

If the problem is the existence of the tag itself, blacklisting would completely solve the problem.

However, as suggested in the comment, there are some questions that "functions" serves as an suitable tag. And after trying to retag some questions in the tag, the retagging work is not completely trivial.


The "functions" tag should be deprecated.

We should add in the tag wiki that users should use a more specific tag, like "algebra-precalculus or elementary-set-theory. This is similar to what we did on "analysis" tag, see here.

One advantage is that it can be implemented easily. The disadvantage is, obviously, that it is not so effective. There are more than 240000 questions tagged with "analysis", and around 100 new questions tagged with "analysis" every week. The tag info page shows that the page has only around 400 views.

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    $\begingroup$ This is not a great solution. To some extent, the discrete-mathematics was "deprecated", and it is still alive and kicking. If the functions tag is so bad, I'd rather put the effort into retagging and blacklisting, with the option of creating new tags to compensate for that. $\endgroup$ – Asaf Karagila Feb 15 '18 at 10:05

I suggest extending functions with the specific self-describing names that the tags might apply to. The extensions serve to more appropriately label the space to a degree whose efficacy varies directly with the propriety of the tags. I suggest prepending the word function to tags that might want to specify so that users may explore the space of tags through autocomplete. This might lead to better questions.


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