@article{ZNSL_1997_246_a7,
     author = {S. E. Kozlov},
     title = {The topology and the {Lorentz-invariant} {pseudo-Riemannian}  metric of the manifold of directions in the
},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {141--151},
     publisher = {mathdoc},
     volume = {246},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1997_246_a7/}
}