1. (a) Einfuhrung in die Quantechemie (Franz Deuticke, Leipzig, 1937), p. 285;
2. Forces in Molecules
3. Ed., The Force Concept in Chemistry (Van Nostrand Reinhold, New York, 1981);
4. The Variational Method in Quantum Chemistry (Academic, New York, 1974);
5. and in Advances in Quantum Chemistry, Ed. (Academic Press, New York, 1985). Vol. 17, pp. 150ff;