1. A. S. Andreev, Stability of Nonautonomous Functional Differential Equations (Ul’yanovsk. Gos. Univ., Ul’yanovsk, 2005) [in Russian].
2. N. N. Krasovskii, Stability ofMotion (Fizmatgiz, Moscow, 1959; Stanford Univ., Palo Alto, CA, 1963).
3. B. S. Razumikhin, Stability of Hereditary Systems (Nauka, Moscow, 1988) [in Russian].
4. J. Hale, Theory of Functional Differential Equations (Springer, New York, 1977; Mir, Moscow, 1984).
5. S. V. Pavlikov, “Constant-Sign Lyapunov Functionals in the Stability Problem for a Functional Differential Equation,” Prikl. Mat. Mekh. 71(3), 377–388 (2007) [J. Appl. Math. Mech. 71 (3), 339–350 (2007)].