2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/154575We prove a generalisation of Elkies' theorem to nonunimodular definite forms (and lattices). Combined with inequalities of Froyshov and of Ozsvath and Szabo, this gives a simple test of whether a rational homology 3-sphere may bound a definite four-manifold. As an example we show that small positive surgeries on torus knots do not bound negative-definite four-manifolds.21 pages, 1 figureGeometric TopologyNumber Theory11H55; 57Q60; 57M27; 57R58.text