2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/76997The authors study singular points of lightlike hypersurfaces of the de Sitter space S^{n+1}_1 and the geometry of hypersurfaces and use them for construction of an invariant normalization and an invariant affine connection of lightlike hypersurfaces.LaTeX, 22 pagesDifferential Geometry53B25text