1. Hehre, W. J., Lathan, W. A., Ditchfield, R., Newton, M. D., Pople, J. A.: ?Gaussian 70? program No. 236, Quantum Chemistry Program Exchange, University of Indiana, Bloomington (1970)
2. Diner, S., Malrieu, J. P., Claverie, P.: Theoret. Chim. Acta (Berl)13, 1 (1969);15, 100 (1969)
3. Pullman, A.: personal communication
4. Laurence, P. R., Thomson, C.: accepted for publication (Theoret. Chim. Acta)
5. Scheraga, H. A.: Adv. in Phys. Org. Chem:6, 103 (1968)