2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/79678Let C be a coalgebra over a field k and A its dual algebra. The category of C-comodules is equivalent to a category of A-modules. We use this to interpret the cotensor product M \square N of two comodules in terms of the appropriate Hochschild cohomology of the A-bimodule M \otimes N, when A is finite-dimensional, profinite, graded or differential-graded. The main applications are to Galois cohomology, comodules over the Steenrod algebra, and the homology of induced fibrations.16 pages, LaTeXRings and AlgebrasAlgebraic Topology16E40 (Primary), 16W30 (Secondary)text