2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/69733To solve problems of Gilbert Baumslag and Hanna Neumann, posed in the 1960's, we construct a nontrivial variety of groups all of whose noncyclic free groups are non-hopfian.17 pagesGroup Theory20E10, 20F05, 20F06text