@AlexanderChervov There was only one open-problem-list question when it was merged, so it was going to be erased anyway (without proper replacement). You are right though, but not necessarily in the way you expect: using open-problems for specific open problems makes it a "meta-tag", the correct usage is what you intend (whether the intent is a list or something else is to be clarified in the question).

By the way, the litmus tests for splitting tags is: (1) Are there many users who would follow one but not the other? (2) Is it obvious for these users which they should follow? If the answer to either of these questions is "no" then 99% of the time the old tag should be kept rather than splitting.

@FrançoisG.Dorais That is strange, since as I've mentioned above, there were 43 open-problems-list in August (according to Google Cache). Wayback Machine shows 42 questions in March.

BTW are you using some kind of moderators' superping above? (I suppose so - otherwise Alxander Chervov would most likely not be pinged.)

Is it possible that we are talking about too different tags - open-problem-list and open-problems-list? (Neither of them exists at the moment.)

The question What are some important but still unsolved problems in mathematical logic? was definitely tagged open-problems-list in the past.

Similarly, Open problems in hyperplane/subspace arrangements? has open-problems-list tag in the Wayback Machine snapshot.

@MartinSleziak Maybe. I recall merging such a tag recently while cleaning up useful tags with low use numbers. Perhaps the other was merged earlier. Unfortunately, there is little tracking of what got merged when, which is one of the reasons it's irreversible.

In any case, using open-problems for specific problems is a meta usage and shouldn't be encouraged. I remember adding the plural form in an attempt to discourage this.

But even if there aren't logs about tag merges, the merge seems like only logical explanation to me. (The Wayback Machine clearly shows that the tag existed a few months ago. There is no trace of the tag at the moment. I doubt that somebody who is not moderator on this site but has "diamond" right would do it.)

@FrançoisG.Dorais I see your point, although I am not sure I agree. (My experience with open-problem tag on math.SE is that seems reasonable.)

Of course, if there is some consensus here on MO, I try to do my best to follow that consensus. However, in this case there does not seem to be any meta discussion about this tag (except for the recent question). And both tag-info and the usage of the tag so far suggest that using it for single open problem is ok.

Maybe it would be worth bringing up as a separate meta question? (It would be more visible than Alexander Chervov's post, which is one answer in a long thread.) OTOH on meta.math.SE I see that there is rather low participation in discussions about tag. Maybe the same is true here - in which case a separate post on meta would probably bring nothing.

In any case, probably the most reasonable thing to do is to wait a bit what Alexander Chervov says, since he brought up the issue.

If adding big-list tag to questions which are actually open problems lists sounds a reasonable thing to do, I can occasionally retag some question from the list found in the Wayback machine.

******

There is also a separate - more general - issue in the comment saying: I do not think moderators should do such things without discussion.

It seems that tags are managed differently on MO than on Mathematics. AFAICT at least some decisions about tags on MO are made by mods alone without being discussed on meta first.

On meta.math.SE we have a lot of discussions about tags on meta, more often than not without reaching any clear conclusion. (Or sometimes the conclusion is that the tag is unsuitable and should be removed - but in the meantime the tag has grown to large number of question.)

Just as an illustration - even this was discussed on that site: Should every new tag be discussed on meta before creation?

So my experience with tags and tag management on that site is quite frustrating. Perhaps it is better if there are few users who are bold enough to make decisions.

@MartinSleziak Yes, the tag management on MO is very different than on Mathematics. There are several reasons for that. For example, the systematic use of broad area tags borrowed from the arxiv on day one brought a lot of stability to the general tagging system here. Mathematics explicitly decided not to use such tags in the early days, which I think was a wise choice since a great deal of users on Mathematics are unfamiliar with the arxiv classification.

In the early days of MO, there was a lot of tagging discussion which helped draw guidelines for what other tags might be useful and appropriate for the site. These days, however, only a handful of users are interested in tagging issues, probably since the system works well enough for everyone.

The main recurring issues are deprecated tags and some borderline meta-tags that exist for historical reasons. open-problems and big-list are two such tags.

Re: For example, the systematic use of broad area tags borrowed from the arxiv on day one brought a lot of stability to the general tagging system here. I made similar point some time ago:

It seems that quid has less optimistic view about how tags work here - it suffices to look at the starred posts - like this one:

chat.stackexchange.com/rooms/info/10243/…

But I certainly agree that there are less problems with tags on MO than on Math.SE. (Maybe it is partially thanks to the fact that MO is smaller site.)

The tag big-list is often used also on math.SE too. It is definitely not going away on MO, considering that MO is much more lenient to soft question than math.SE. (At least in the recent years, soft questions on math.SE are very often closed. It used to be different in the past.)

Is seems that basically what we are both saying is the two sites are different. (Both in general an din tag-related issues.) Which is not that surprising.

This was the message I wanted to post there. (I copy-pasted wrong link, sorry.)

Looking back at those old discussions with quid, at least I feel a bit useful. (Since I try to add top-level-tags when I see a new post which does not have one. And sometimes, when I am not sure which tag to use, I ask here.)

Ok, I'll have to go. Thanks for your responses!

I miss quid! He's quite right even though his rants should always be taken with a grain of salt.

@FrançoisG.Dorais BTW he is running in the mod elections on math.SE.

But you probably noticed it. (I do not know how much people from MO follow Mathematics site, but election is an event which probably does not go unnoticed.)

Since you mentioned meta tags, there are quite a few on math.SE, too.

Since the possibility that we are talking about two different tags was mentioned, I should probably add that the original post contained open-problem-list. Since I thought that it is a typo, I edited it to open-problems-list. (For the latter I at least know that it existed - from Wayback Machine and Google Cache.)

I will just mention that the bookmarked conversation (=second link) can be extended to contain more messages. (In case the discussion continues here.)

There were many questions tagged open-problems-list , I think 43 is right number from Martin, most of "problems in RT, AG, DG ...." were tagged like that and imho it was quite convenient - just press it and get all the list of open problems present at MO, I am afraid that cannot be done with the help of two tags like biglist+openproblem - you cannot press it. So I would be happy to see it reversed.

How is it possible to edit tags and not to pop-up the question to the front page ? Is it only moderators option ?

@AlexanderChervov I will leave the discussion about the tag to you and François G. Dorais, but I can at least answer the question about "only moderator option". There is not such possibility (neither for moderators nor for regular users). It was discussed a few times but never implemented.

For example “Silent” Edits for MO? and Minor edits, subject to review on this meta or Allow non-bumping minor edits, but review them on /review on meta.SE.

So, for example, a moderator could be able to replace all occurrences of open-problems by open-problems-list or some other name without bumping anything. But if we want some change which influences only some questions (not all questions in a certain tag), this can only be done manually.