1. Jordan C. Calculus of Finite Differences Chelsea Publishing Company New York 1950.
2. Die gewohnlichen und partiellen Differenzengleichungen der Baustatik, Julius Springer;Bleich F.;Berlin,1927
3. v. K3.rman T. Mathematical Methods in Engineering McGraw-Hill
4. Company New York 1940 pp. 437-451.
5. Bleich F. Buckling Strength of Metal Structures McGraw-Hill Company New York 1952 pp. 260 and 275.