Projections of timelike surfaces in the de Sitter space

摘要

We study in this paper projections of embedded timelike hypersurfaces M in S_1~n along geodesics. We deal in more details with the case of surfaces in S_1~3, characterise geometrically the singularities of the projections and prove duality results analogous to those of Shcherbak for central projections of surfaces in R P~3.