Differential geometry of non-linear non-holonomic manifolds in the three- dimensional Euclidean space. B. Вагнер Matematiceskij sbornik
Differential geometry of the family of R k ’s in R n and of the family of totally geodesic S k - 1 ’s in S n - 1 of positive curvature B. Вагнер — 1942 Matematiceskij sbornik