2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/88694We discuss some issues about probability in quantum mechanics, with particular emphasis on the GHZ theorem. We propose the usage of nonmonotonic upper probabilities as a tool to derive consistent joint upper probabilities for systems where only contextual hidden variables are possible.LaTeX2e, 13 pages, to appear in the proceedings in honor of Arthur FineQuantum Physicstext