@article{INTG_1985_17_a2,
     author = {V. V. Nikulin},
     title = {Local invariants of 4-dimensional {pseudo-Riemannian} manifolds with {a~Lorentz} metric},
     journal = {Itogi Nauki i Tekhniki. Seriya Problemy Geometrii. Trudy Geometricheskogo Seminara},
     pages = {87--130},
     publisher = {mathdoc},
     volume = {17},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/INTG_1985_17_a2/}
}