2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/91910A bistochastic matrix is a square matrix with positive entries such that rows and columns sum to unity. A unistochastic matrix is a bistochastic matrix whose matrix elements are the absolute values squared of a unitary matrix. We can now ask questions such as when a given bistochastic matrix is unistochastic. I review these questions: Why they are asked, why they are difficult to answer, and what is known about them.8 pages, contribution to the Second Vaxjo Conference of Quantum Theory: Reconsideration of FoundationsQuantum Physicstext