1. See the reviews in “Positron Solid-State Physics — Proc. Int. School E. Fermi,” edited by W. Brandt and A. Dupasquier (North-Holland, Amsterdam, 1983).
2. See also the reviews in the Proceedings of the International Conferences on Positron Annihilation (ICPA) published every three years — “Positron Annihilation — ICPA-7,” edited by P. C. Jain, R. M. Singru and K. P. Gopinathan (World Scientific, Singapore, 1985); “Positron Annihilation — ICPA-8,” edited by M. Dorikens, L. Dorikens-van Praet and D. Segers (World Scientific, Singapore), to be published 1989.
3. Review by A. P. Mills, Jr., in Ref. 1, p. 432.
4. Review by P. J. Schultz and K. G. Lynn, Rev. Mod. Phys. 60, 701, (1988).
5. See the review by R. Paulin in Ref. 1, p. 565.