1. Babu?ka, I.: Survey lectures on the mathematical foundations of the finite element method. The mathematical foundations of the finite element method with applications to partial differential equations (A.K. Aziz, ed.), pp. 5?359. New York: Academic Press 1973
2. Tech. Note BN-853;I. Babu?ka,1977
3. Bramble, J.H., Osborn, J.E.: Rate of convergence estimates for nonselfadjoint eigenvalue approximation. Math. Comput.27, 525?549 (1973)
4. Chatelin, F.: La méthode de Galerkin. Ordre de convergence des éléments propres. C.R. Acad. Sci. Paris Sér. A278, 1213?1215 (1974)
5. Chatelin, F., Lemordant, J.: Error bounds in the approximation of eigenvalues of differential and integral operators. J. Math. Anal. Appl. (to appear)