1. A.G. Reyman, M.A. Semenov-Tian-Shansky, Reduction of Hamiltonian systems, affine Lie algebras and Lax equations, Invent. Math., 1979, Vol. 54, N1, 81–100.
2. A.A. Kirillov, Unitary representations of the group of diffeomorphisms and of certain of its subgroups, Preprint of the Institute of Applied Mathematics, 1974, N82, (in Russian).
3. A.A. Kirillov, Representations of some infinite dimensional Lie groups, Vestnik MGU, ser. math., 1974, N1, 75–83 (in Russian).
4. A.A. Kirillov, On invariant differential operators on geometrical quantities. Funkt. anal. i ego pril., 1977, 11, N2, 39–44 (in Russian).
5. Th. Bröcker, L. Lander, Differential germs and catastrophes, London Math. Soc. Lecture Notes series, 17. Cambridge Univ. Press, 1975.