2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/33780We examine some kinds of discrete symmetries which are dynamically preserved, using the (generalized) Gowdy models of the first kind.6 pages, 2 figures, LaTeX. To appear in the proceedings of JGRG10, Osaka, Sept. 11-14, 2000General Relativity and Quantum Cosmologytext