[1] Kurzweil J.: On a system of operator equations. Journ. Diff. Eq. 11 (1972), pp. 364-375. MR 0310390 | Zbl 0211.17701

[2] Kurzweil J.: Solutions of linear nonautonomous functional differential equations which are exponentially bounded for $t \rightarrow -\infty$. Journ. Diff. Eq. 11 (1972), pp. 376-384. MR 0310396

[3] Friedman A.: Partial differential equations of parabolic type. Prentice-Hall Inc., New York 1964. MR 0181836 | Zbl 0144.34903

[4] Ladyzenskaya O. A., Solonnikov V. A., Uralceva N. N.: Linear and quasilinear equations of parabolic type. Nauka, Moskva 1967. (Russian.)