1. N. N. Bogolyubov and Yu. A. Mitropol’skii, Asymptotic Methods in the Theory of Nonlinear Oscillations [in Russian], Nauka, Moscow (1963).
2. Yu. A. Mitropol’skii and O. B. Lykova, Integral Manifolds in Nonlinear Mechanics [in Russian], Nauka, Moscow (1973).
3. D. Henry, Geometric Theory of Semilinear Parabolic Equations, Springer, Berlin (1981).
4. M. P. Vishnevskii, Invariant Sets of Nonlinear Parabolic Systems. Some Applications of Functional Analysis to Problems of Mathematical Physics [in Russian], Institute of Mathematics, Siberian Division of the Academy of Sciences of the USSR, Novosibirsk (1986), pp. 32–56.
5. V. N. Levitan and V. V. Zhikov, Almost-Periodic Functions and Differential Equations [in Russian], Moscow University, Moscow (1978).