L. Ezhova-Guseva, T. Klimanova, and E. Yasinskaya, “Metric invariants of equations of Hermitean quadrics in unitary non-Euclidean and semi- non-Euclidean spaces”, LMJ, vol. 6, no. 4, pp. 503–513, Dec. 1966, doi: 10.15388/LMJ.1966.19749.