2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48036The Green's function formalism for neutrino mixing is presented and the exact oscillation formula is obtained. The usual Pontecorvo formula is recovered in the relativistic limit.4 pages, LaTeX (need sprocl.sty). To appear in the Proceedings of the 6th International Symposium on Particles, Strings and Cosmology (PASCOS 98), Boston, 22-27 March 1998High Energy Physics - Phenomenologytext