E. B. Vinberg, S. G. Gindikin, “Degeneration of Horospheres in Spherical Homogeneous Spaces”, Funct. Anal. Appl., 52:2 (2018), 83–92
V. S. Zhgun, “Malaya gruppa Veilya i mnogoobrazie vyrozhdennykh orisfer”, Chebyshevskii sb., 16:4 (2015), 164–187
Losev I.V., “Algebraic Hamiltonian actions”, Mathematische Zeitschrift, 263:3 (2009), 685–723
I. V. Losev, “Combinatorial Invariants of Algebraic Hamiltonian Actions”, Mosc. Math. J., 8:3 (2008), 493–519
D. A. Timashev, “Equivariant symplectic geometry of cotangent bundles. II”, Mosc. Math. J., 6:2 (2006), 389–404