2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/117156This paper has been withdrawn by the authors, due to a flaw in the proof of Theorem 1. This preprint is superseded by quant-ph/0610027, where a correct proof can be found. Thanks to Rainer Siegmund-Schultze for spotting the error.Withdrawn due to flaw in proof of Theorem 1. Superseded by pre-print quant-ph/0610027Quantum Physicstext