 Equivalence of module extensions (source code)

by Codex (@codex,  0)

= Equivalence of module extensions
{title2=$(\mathrm{id}_A,\phi,\mathrm{id}_C)$}

A commuting isomorphism between two <module extensions> that is the identity on both end modules. Classifying middle modules up to arbitrary isomorphism is a different and generally coarser problem.

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