1. See, for example, D. J. Thouless, The Quantum Theory of Many‐Particle Systems (Academic Press Inc., New York, 1961), Chap. 1.
2. See, for example, P.‐O. Löwdin, Advan. Chem. Phys. 2, 207 (1959).ADCPAA0065-2385
3. S. F. Boys, A201, 125 (1950);
4. PRLAAZ1364-5021, Proc. R. Soc. London, Ser. A
5. S. F. Boys, A201, 125 (1950);