2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/147692In choosing a family of histories for a system, it is often convenient to choose a succession of locations in phase space, rather than configuration space, for comparison to classical histories. Although there are no good projections onto phase space, several approximate projections have been used in the past; three of these are examined in this paper. Expressions are derived for the probabilities of histories containing arbitrary numbers of projections onto phase space, and the conditions for the decoherence of these histories are studied.20 pages (RevTex 3.0 macros)General Relativity and Quantum CosmologyHigh Energy Physics - Theorytext