@article{DAN_1967_176_1_a13,
     author = {R. I. Khrapko},
     title = {Defining the space type on {Petrov's} classification},
     journal = {Doklady Akademii Nauk},
     pages = {56--57},
     publisher = {mathdoc},
     volume = {176},
     number = {1},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1967_176_1_a13/}
}