1. Lectures on Elliptic Boundary Value Problems;Agmon,1965
2. Behavior of the error of the approximate solutions of boundary value problems for linear elliptic operators by Galerkin's and finite difference methods;Aubin;Ann. Scuola Norm. Pisa,1967
3. Numerical Processes in Differential Equations;Babuška,1966
4. On eigenvalue distributions for elliptic operators without smooth coefficients;Beals;Bull. Am. Math. Soc.,1966
5. An asymptotic formula for the eigenvalues of the Laplace operator in an unbounded domain;Clark;Bull. Am. Math. Soc.,1966