2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/77415We show that the obstruction to the existence of a strict symmetric monoidal structure on a monoidal stack $\cal C$ is determined by a commutator biextension associated to $\cal C$, and that this biextension is alternating under an additional hypothesis. The analogous construction for monoidal 2-stacks is described, together with the corresponding generalizations of the concept of a biextension.LaTeX, xy-pic, 38 pagesCategory TheoryAlgebraic Geometrytext