@article{DAN_1968_180_5_a23,
     author = {M. Sh. Yakupov},
     title = {Einstein's spaces of the second order of immersion},
     journal = {Doklady Akademii Nauk},
     pages = {1096--1098},
     publisher = {mathdoc},
     volume = {180},
     number = {5},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_180_5_a23/}
}