[1]
B. A. . Rozenfeld, L. M. . Karpova, and L. P. Andreeva, “Metrical invariants and covariants of couples of planes in the quasielliptic space”, LMJ, vol. 4, no. 2, pp. 241–253, Jun. 1964, doi: 10.15388/LMJ.1964.19504.