Time-like hypersurfaces in de Sitter space and Legendrian singularities

We construct a basic framework for studying the extrinsic differential geometry on time-like hypersurfaces in the de Sitter space from the viewpoint of the theory of Legendrian singularities. As an application, we study the contact of time-like hypersurfaces with flat totally umbilic time-like hypersurfaces in the de Sitter space. __________ Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 33, Suzdal Conference-2004, Part 1, 2005.