1. Moser, J., The Analytical Invariants of an Area-preserving Mapping near a Hyperbolic Fixed Point, Comm. Pure Appl. Math., 1956, vol. 9, no. 4, pp. 673–692.
2. Treschev, D.V., Quantum Observables: An Algebraic Aspect, Proceedings of the Steklov Institute of Mathematics, 2005, pp. 211–244.
3. Egorov, Ju.V., The Canonical Transformations of Pseudodifferential Operators, Usp. Mat. Nauk, 1969, vol. 24, pp. 235–236.
4. Hörmander, L., Fourier Integral Operators. I, Acta Math., 1971, vol. 127, pp. 79–183.
5. Duistermaat, J. J. and Hörmander, L., Fourier Integral Operators. II, Acta Math., 1972, vol. 128, pp. 183–269.