1. Courant, R., andD. Hilbert: Methods of Mathematical Physics, Vol. I. New York 1953.
2. Dunford, N., andJ. T. Schwartz: Linear Operators, Part I. New York 1958.
3. Halmos, P. R.: Finite-Dimensional Vector Spaces. Princeton 1958.
4. Hille, E., andR. S. Phillips: Functional Analysis and Semi-groups. Amer. Math. Soc. Colloquium Publ., Vol. XXXI, 1957.
5. Lax, P. D., andR. D. Richtmyer: Survey of the stability of linear finite difference equations. Comm. Pure Appl. Math.7, 267?293 (1956).