2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/12328The post-Newtonian approximation of general relativistic Liouville's equation is presented. Two integrals of it, generalizations of the classical energy and angular momentum, are obtained. Polytropic models are constructed as an application.16 Pages, 2 Tables, To appear in Astronomy and Astrophysics JournalAstrophysicstext