1. BABUSKA, I., AZIZ, A.K.: Survey lectures on the mathematical foundations of finite element method. Chapt.11 (with G.FIX). In: The Mathematical Foundations of the Finite Element Method with Applications to Partial Differential Equations. Part I. Ed. K. Aziz. Academic Press, New York, London (1972)
2. DOUGLAS, Jr. J., DUPONT, T.: Galerkin methods for parabolic equations with nonlinear boundary conditions. Numer. Math.20, 213?237 (1973)
3. FIX, G., NASSIF, N.: On finite element approximation to time dependent problems. Numer. Math.19, 127?135 (1972)
4. KATO, T.: Perturbation Theory for Linear Operators. Springer Verlag, Berlin-Heidelberg-New York (1966)
5. KEEIN, S.G.: Linear differential equations in Banach spaces. Translations of Mathematical Monographs, Vol.29. American Mathematical Sociaty, Providence (1971)