1. L. Van Hove:Phys. Rev.,95, 249 (1954);
2. P. Nozières:Le problème à N corps (Paris, 1963), Chap. 2.
3. B. Bosco andP. Quarati:Nuovo Cimento,33, 527 (1965);
4. P. Quarati:Multipolar sum rules for electromagnetic interactions with nuclei, submitted toNuovo Cimento.
5. W. C’yz:Phys. Rev.,134, 2141 (1963).