@article{PIM2_1998__63(77)_258078,
     author = {Akivis, M.A. and Goldberg, V.V.},
     title = {Singular points of lightlike hypersurfaces of the de {Sitter} space.},
     journal = {Publications de l 'Institut Math\'ematique. Nouvelle S\'erie},
     pages = {81},
     publisher = {mathdoc},
     volume = {63(77)},
     year = {1998},
     zbl = {0949.53015},
     language = {en},
     url = {https://geodesic-test.mathdoc.fr/item/PIM2_1998__63(77)_258078/}
}