1. Allen D. N. de G. 1954 Relaxation methods. New Y ork: McGraw-Hill.
2. Courant R . & H ilbert D. 1953 science. Methods oj mathematical physivol. 1. New Y ork: In te r
3. Kellogg O. D. 1929 Foundations of potential theory. B erlin: Springer.
4. Love A. E . H . 1952 Theory of elasticity (4th ed.). Cambridge U niversity Press.
5. M uskhelishvili N. I. 1953a Singular integral equations. Groningen: Noordhoff.