2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/115502It is proved that the third Mac Lane cohomology group of a ring R with coefficients in a bimodule B classifies categorical rings having R as the ring of isomorphism classes of objects and B as the bimodule of automorphisms of the neutral object.K-Theory and Homology18G60; 16E40text