@article{IM2_1967_1_6_a9,
     author = {L. A. Nazarova},
     title = {Representation of a tetrad},
     journal = {Izvestiya. Mathematics },
     pages = {1305--1321},
     publisher = {mathdoc},
     volume = {1},
     number = {6},
     year = {1967},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1967_1_6_a9/}
}