2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/93455We illustrate two simple spin examples which show that in the consistent histories approach to quantum mechanics one can retrodict with certainty incompatible or contradictory propositions corresponding to non-orthogonal or, respectively, orthogonal projections. V.2 vs. V1: The example previously quoted as "d'Espagnat's example" is now properly quoted as "Griffiths' example". A reference to a previous work by Aharonov and Vaidman is added.4 pages, RevTeX, 3 diagrams processed by TeXQuantum Physicstext