2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/100081This paper has been withdrawn. See quant-ph/0408115: G. M. D'Ariano, P. Perinotti and P. Lo Presti, "Classical randomness in quantum measurements"This paper has been superseeded by quant-ph/0408115Quantum Physicstext