2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/63240We prove a result concerning formality of the pull-back of a fibration. Our approach is to use bar complexes in the category of commutative differential graded algebras. As an application, we generalize an old result of Baum and Smith.8 pages, no figuresAlgebraic Topologytext