1. R. S. Ismagilov, "On unitary representations of the diffeomorphism group of the circle," Funkts. Anal. Prilozhen.,5, No. 3, 45–53 (1971).
2. A. M. Vershik, I. M. Gel'fand, and M. I. Graev, "Representations of a group of diffeomorphisms," Usp. Mat. Nauk,30, No. 6, 3–50 (1975).
3. A. M. Vershik, "A description of the invariant measures for the actions of certain infinite-dimensional groups," Dokl. Akad. Nauk SSSR,218, No. 4, 749–752 (1974).