9:50 AM
@MartinSleziak The suggested edit was rejected. However, even failed attempt to create the tag-excerpt should prevent the tag from getting removed even if it has only one question. mathoverflow.net/posts/389122/revisions mathoverflow.net/posts/389121/revisions
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So this is interesting. Technically speaking, that tag does have a wiki. It's just blank. The wiki's post ID is assigned to the tag, and you can view the revision history showing it was created shortly after the post was created: https://mathoverflow.net/posts/295234/revisions Having the wiki cr...

John Pardon, I see that you have created (legendrian-submanifolds) tag. It might be useful to create also tag-wiki or at least tag-excerpt. It might help other users to use the tag correctly. (This is probably not a problem here, since the tag name seems to be descriptive enough.) Another reason is that the tags used on only one question are automatically deleted after six months unless they have tag-wiki. — Martin Sleziak 28 secs ago
@MartinSleziak The tag no longer exists. It is not shown in the revision history, so either it was removed by a script or merged by a mod into another tag.
@MartinSleziak The tag is gone, too. Nothing shown in the revision history.
@MartinSleziak The tag now has four questions.
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I know that not every finitely-presented group may be embedded into a one-relator group, for example because of a theorem of Magnus stating that the word problem is solvable in one-relator groups. But does there is a great amount of finitely-generated groups embeddable into a one-relator group? ...

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I've read that every finitely generated one relator group embeds in a two generator one relator group, and that this fact follows from the Freiheitssatz. Unfortunately, the only proof I can find of this fact applies B.H. Neumann's proof for denumerable n-relator groups, and it doesn't seem to u...

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Roughly speaking, I want to know whether one-relator groups only have 'obvious' free splittings. Consider a one-relator group $G=F/\langle\langle r\rangle\rangle$, where $F$ is a free group. Is it true that $F$ splits non-trivially as a free product $A * B$ if and only if $r$ is contained in...

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Is there a one-relator group with property (T)? That is, is there an $n > 2$, and some $x \in F_n$ (the free group on $n$ generators) such that the quotient of $F_n$ by the normal subgroup generated by $x$ has Kazhdan's property $\mathrm{(T)}$ ?