1. Agmon, S., Lectures on Elliptic Boundary Value Problems. Princeton: Van Nostrand, 1965.
2. Birkhoff, G., M.H. Schultz, & R.S. Varga, Piecewise hermite interpolation in one and two variables with applications to partial differential equations. Numer. Math. 11, 232–256 (1968).
3. Bramble, J.H., & B.E. Hubbard, A priori bounds on the discretization error in the numerical solution of the Dirichlet problem. Contributions to Differential Equations 2, 229–252 (1963).
4. Bramble, J.H., & B.E. Hubbard, A theorem on error estimation for finite difference analogues of the Dirichlet problem for elliptic equations. Contributions to Differential Equations 2, 319–340 (1963).
5. Bramble, J. H., & B. E. Hubbard, Approximation of solutions of mixed boundary value problems for Poisson's equation by finite differences. J. Association for Computing Machinery 12, 114–123 (1965).