@article{DAN_1957_113_3_a3,
     author = {N. I. Kovantsov},
     title = {A ruled surface geometry analogue to a triorthogonal system of surfaces},
     journal = {Doklady Akademii Nauk},
     pages = {497--500},
     publisher = {mathdoc},
     volume = {113},
     number = {3},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_113_3_a3/}
}