@article{DAN_1957_117_2_a3,
     author = {S. E. Karapetyan},
     title = {Second order {Lie} surface for ruled surfaces of congruence},
     journal = {Doklady Akademii Nauk},
     pages = {177--179},
     publisher = {mathdoc},
     volume = {117},
     number = {2},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_117_2_a3/}
}