2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148508We study the general theorem about gravitational lensing which states the relationship between the numbers of images with different parities. Our formulation allows an extension to the nontransparent and singular model.9pages, aastex, 2 figures, typing and grammatical errors correctedAstrophysicstext