2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/160352We generalize the notion of proper stack introduced by Kashiwara and Schapira to the case of a general site, and we prove that a proper stack is a stack.8 pages, uses xy-pic. This is a revised versionAlgebraic Geometry14A20; 18D30, 18F10text