1. B. Helffer, Théorie spectrale pour des operateurs globalement elliptiques, in Asterisque (Paris, 1984), Vol. 112.
2. F. A. Berezin and M. A. Shubin, Scrödinger Equation (Izd. Moskov. Univ., Moscow, 1983; Kluwer, Dordrecht, 1991).
3. A. N. Shiryaev, Probability: I (MTsNMO, Moscow, 2004) [in Russian].
4. V. V. Kozlov, Heat Equilibrium according to Gibbs and Poincaré (Institute for Computer Studies, Moscow-Izhevsk, 2002) [in Russian].