@article{DAN_1970_192_6_a15,
     author = {L. B. Grigoryeva},
     title = {Chronometrically invariant representation of the classification of {Petrov's} gravitational fields},
     journal = {Doklady Akademii Nauk},
     pages = {1251--1254},
     publisher = {mathdoc},
     volume = {192},
     number = {6},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_192_6_a15/}
}