1. Babuska, I.: Error bounds for the finite element method. Numer. Math.16, 322?333 (1971)
2. Proc. of the Conf. on the Mathematical Foundations of the Finite Element Method;I. Babuska,1973
3. Fried, Isaac, Yang, Shok Keng: Best finite element distribution around a singularity. AIAA Journal10, 1244?1246 (1972)
4. Lions, J. L., Magenes, E.: Problemes aux limites non homogenes et applications, vol. 1. Paris: Dunod 1968
5. Strang, G., Fix, G.: A fourier analysis of the finite element method. Proc. of the CIME summer school (1971), to appear