2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/92108Two new formulations of Bell's theorem are given here. First, we consider a definite set of two entangled photons with only two polarization directions, for which Bell's locality assumption is violated for the case of perfect correlation. Then, using a different approach, we prove an efficient Bell-type inequality which is violated by some quantum mechanical predictions, independent of the efficiency factors.15 pages, 2 tables, no figure. Last version, to appear in Fortschritte der PhysikQuantum Physicstext