2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/98443We first show that co-amenability does not pass to subgroups, answering a question asked by Eymard in 1972. We then address co-amenability for von Neumann algebras, describing notably how it relates to the former.final version (minor changes)Group TheoryOperator Algebras43A07; 43A85; 46Ltext