Occasionally I have seen that for low-level questions (such as introductory calculus exercises or similar level) some user replaced the tags by the tag1 - to indicate that the question is off-topic. (I will not be able to find an example easily, since such questions are typically removed by roomba after a certain time. So you'll probably have to rely on my word, that I indeed remember seeing a few such edits.) I suppose that in some of those cases other users might have voted to migrate to Mathematics site.

If a migrated question has only tags which do not exist on the target site, then the migration is rejected. The minor exception are intrinsic tags - it could be said that those tag "exist without being used".2

  • Should we request from Mathematics site to add the tag to intrinsic tags, so that a migration of a question having only this tag goes through? (Although I can imagine some valid reasons against doing this, so it is possible that even if the consensus here is that it should be an intrinsic tag, moderators from Mathematics or Stack Exchange staff handing the request might say no.)
  • Would it be better in situation like this to use rather then (tag-removed). The tag (gm.general-mathematics) already is an intrinsic tag on Mathematics, see here: Which are blacklisted tags and blacklisted phrases? and MO-MSE tag incompatibility (Mathematics Meta).

As an additional question: Could somebody with sufficient privileges check whether the reason for rejecting migration is often the tag incompatibility.3

1 Some basic info about the tag can be found in the tag-info for this tag, in the answers to 'Tag-removed' tags where they possibly shouldn't be and also in chat: Purpose of (tag-removed) tag and More details about (tag-removed) tag.

2Here are some related discussions on this meta: How to (re)tag such that migration works? and Potential “technical” obstacle to migrations, and suggestion for a solution. Some explanation what intrinsic tags are be found in this answer: Drop or change automatic migration-rejection based on non-existing tags.

3I do not have sufficient reputation to see the tools (which include migration tab) here on MathOverflow. By checking on Mathematics I can see that, in the last 90 days, 30% of migrations from MathOverflow were rejected. But I do not see specific reasons why there were rejected. (And, in fact, I am not even sure whether migrations that fail on grounds of tag incompatibility are shown here or they are treated as if they were never migrated. It seems that in the revision history and timeline nothing about rejected migration is shown in the example from an older discussion. The example linked in this Meta MathOverflow discussion does not show anything about the rejected migration in revision history/timeline.)

  • $\begingroup$ Whether having the tag (tag-removed) is actually needed on this site is a separate question - but that's probably discussion for another time. At the moment the tag exists and since it is sometimes used for questions which belong on a different site, it is reasonable to ask whether the tag influences migration. $\endgroup$ Apr 23, 2018 at 5:16
  • 1
    $\begingroup$ The typical use of "tag-removed" is of a highly off-topic question with fantasist tags (a frequent one being algebraic-geometry, say for some high school homework question). These questions are not prone to be migrated. This also affects pure spams, which use random tags. Once another user changed "set-theory" to 'tag-removed" a question about terminology of partially defined functions, and I reverted (while the question was off-topic but reasonable for MathSE- I think it was closed): tag-removed is unnecessary there and set-theory wasn't that bad. $\endgroup$
    – YCor
    Apr 27, 2018 at 2:26


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