2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36234An effective time--dependent cosmological constant can be recovered for higher--order theories of gravity by extending to these ones the no--hair conjecture. The results are applied to some specific cosmological models.6 pages, Latex, ISMC'98 (Potsdam), sprocl.styGeneral Relativity and Quantum Cosmologytext