2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54299The holomorphy of the superpotential along with symmetries gives very strong constraints on any stringy non-perturbative effects. This observation suggests an approach to string phenomenology. (Presented at ``Strings 95'', March 1995.5 pages compressed postscriptHigh Energy Physics - Theorytext