Ezhova-Guseva, L., et al. “Metric Invariants of Equations of Hermitean Quadrics in Unitary Non-Euclidean and Semi- Non-Euclidean Spaces”. Lithuanian Mathematical Journal, vol. 6, no. 4, Dec. 1966, pp. 503-1, https://doi.org/10.15388/LMJ.1966.19749.