2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/155138It is shown that the `arrow of time' operator, M_F, recently suggested by Strauss et al., in arXiv:0802.2448v1 [quant-ph], is simply related to the sign of the canonical `time' observable, T (apparently first introduced by Holevo). In particular, the monotonic decrease of < M_F > corresponds to the fact that < sgn T > increases monotonically with time. This relationship also provides a physical interpretation of the property M_F < 1. Some further properties and possible generalisations are pointed out, including to almost-periodic systems.Further propeties, generalisation to almost periodic systems, ref added, minor corrections, bad punQuantum Physicstext