2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/63460In this paper we pose and answer the following question in a few different contexts: Given a homomorphism f:L_1 --> L_2 of a ``lattices'' that ``reduces mod p'' for almost all primes p, is f ``algebraic''? For instance the lattices may be the Mordell-Weil lattices of rational points of abelian varieties over Q, or arithmetic groups etc. Implicit in an affirmative answer to the question for Mordell-Weil lattices is a novel criterion for abelian varities to be isogenous.Number Theorytext