1. H. Machleidt, invited paper at this symposium.
2. G. A. MIller, invited paper at this symposium.
3. J. de Swart, invited paper at this symposium.
4. R. Vinh Mau, in Mesons in Nuclei, edited by M. Rho and D. Wilkinson (North-Holland, New York, 1979), Vol. I, p. 151.
5. B. D. Serot and J. D. Walecka, Phys. Lett. 87B, 172 (1979) and references therein.