1. V. P. Maslov, Perturbation Theory and Asymptotic Methods (Mosc. State Univ., Moscow, 1965) [in Russian].
2. V. P. Maslov, The Complex Method VKB in Nonlinear Equations (Nauka, Moscow, 1977) [in Russian]; V.P. Maslov, Operator Methods (Nauka, Moscow, 1977) [in Russian].
3. V. Witt, Phys. Rev. 162, 1195 (1967); B. De Witt, Dynamic Theory of Groups and Fields (Gordon Breach, New York, 1965; Nauka, Moscow, 1987).
4. R. Dashen, B. Hasslasher, and A. Neveu, Phys. Rev. D 10, 4114 (1974); J. Goldstone and R. Jackiw, Phys. Rev. D 11, 1486 (1975).
5. R. Jackiw, Rev. Mod. Phys. 49, 681 (1977).