@article{DAN_1975_223_1_a17,
     author = {L. P. Grishchuk and M. V. Sazhin},
     title = {Petrov classification of standing and traveling gravitational waves},
     journal = {Doklady Akademii Nauk},
     pages = {72--75},
     publisher = {mathdoc},
     volume = {223},
     number = {1},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1975_223_1_a17/}
}