@article{UZKU_1954_114_2_a6,
     author = {P. I. Petrov},
     title = {On differential invariants of conformally flat three-dimensional {Riemannian} spaces},
     journal = {U\v{c}\"enye zapiski Kazanskogo universiteta. Seri\^a Fiziko-matemati\v{c}eskie nauki},
     pages = {109--122},
     publisher = {mathdoc},
     volume = {114},
     number = {2},
     year = {1954},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/UZKU_1954_114_2_a6/}
}