2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34665We present a general formalism for describing singular hypersurfaces in the Einstein theory of gravitation with a Gauss--Bonnet term. The junction conditions are given in a form which is valid for the most general embedding and matter content and for coordinates chosen independently on each side of the hypersurface. The theory is applied to both a time--like and a light--like hypersurface in brane--cosmology.11 pages, Latex fileGeneral Relativity and Quantum Cosmologytext