Homological full-and-faithfulness of comodule inclusion and contramodule forgetful functors

This paper establishes that for a conilpotent coalgebra CC, the inclusion of comodules into CC^*-modules and the forgetful functor from contramodules to CC^*-modules both induce fully faithful triangulated functors on appropriate bounded derived categories if and only if the Ext-groups ExtCn(k,k)\operatorname{Ext}_C^n(k,k) are finite-dimensional for all n0n \ge 0, a condition the authors term "weakly finitely Koszul."

Leonid Positselski2026-03-04🔢 math