1. J. Greenstadt, "On the Reduction of Continuous Problems to Discrete Form", IBM Jour. of Res., Vol. 3, p. 355 (Oct. 1959).
2. G. Birkhoff, C. de Boor, B. Swartz and B. Wendroff, "Rayleigh-Ritz Approximation by Piecewise Cubic Polynomials", Jour. SIAM, Vol. 3, p. 188 (1966).
3. O. C. Zienkiewicz, The Finite Element Method, McGraw-Hill Ltd. London 1967.
4. J. Hersch, "Equations Differentielles et Fonctions de Cellules", C. R. Acad. Sci. Paris, Vol. 240, p. 1602 (1955).
5. J. Greenstadt, "Cell Discretization III, Treatment of Discrete Equations" IBM NY Sci. Centre Report, No. 320–2914 (Sept. 1967).