8:03 AM
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I propose adding n cat lab tag as in https://ncatlab.org/nlab/show/HomePage. As https://ncatlab.org/nlab/show/HomePage has large amount of mathematics used as reference and/or as in learning for the first time I guess it would be useful to have a tag. Questions in this tag should be restricte...

1 hour later…
9:07 AM
@MartinSleziak The tag has been removed by François G. Dorais.

4 hours later…
1:18 PM
I am not sure whether suitable top-level tag for A question concerning a short exact sequence with an action would be or . (It is related both to groups and modules.) The tag seems a reasonable fit for that question, too.
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Let $A$ and $D$ be two abelian groups and $B,C$ be two non-abelian groups. Also, let $C$ acts on $A,B,D$. Let $0\to A \xrightarrow{f}B\xrightarrow{g}C\to 0$ be a short exact sequence of groups in which the action of $C$ commutes with maps $f$ and $g$ ($C$ acts on itself trivially). Also, let...