2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/91265We expand on a recent development by Hardy, in which quantum mechanics is derived from classical probability theory supplemented by a single new axiom, Hardy's Axiom 5. Our scenario involves a `pretend world' with a `pretend' Heisenberg who seeks to construct a dynamical theory of probabilities and is lead -- seemingly inevitably -- to the Principles of Quantum Mechanics.15 pages, 0 figuresQuantum Physicstext