1. L. M. Lyapunov, General Problem of Stability of Motion (GITTL, Moscow, 1950) [in Russian].
2. L. Cesari, Asymptotic Behavior and Stability Problems in Ordinary Differential Equations (Berlin, 1959; Mir, Moscow, 1964).
3. L. Ya. Adrianova, Introduction to the Theory of Linear Systems of Differential Equations (Izd. St. Petersburg Univ., St. Petersburg., 1992) [in Russian].
4. V. A. Yakubovich and V. M. Starzhinskii, Linear Differential Equations with Periodic Coefficients and Their Applications (Nauka, Moscow, 1972) [in Russian].
5. R. Bellman, Stability Theory ofDifferential Equations (McGraw-Hill,New York–Toronto–London, 1953; Inostr. Lit., Moscow, 1954).