1. Babuška, I.: Error-bounds for finite element method. Numer. Math.16, 322–333 (1971)
2. Babuška, I., Aziz, A.K.: Survey Lectures on the Mathematical Foundation of the Finite Element Method. In: The mathematical foundations of the finite element method with applications to partial differential equations, A.K. Aziz, ed. pp. 5–359, New York: Academic 1973
3. Boor, C. de: The Method of projections as applied to the numerical solution of two point boundary value problems using cubic splines. Thesis, University of Michigan, 1966
4. Bramble, J., Hilbert, S.: Estimation of linear functionals on Sobolev spaces with application to Fourier transforms and spline interpolation. SIAM J. Numer. Anal.,13, 185–197 (1976)
5. Douglas, J., Jr., Dupont, T., Wahlbin, L.: OptimalL ∞ error estimates for Galerkin approximations to solutions of two-point boundary value problems. Math. Comp.29, 475–483 (1975)