1. Bershad, N. J., and Rockmore, A. J., IEEE Trans., IT, 20, 112–113 (1974).
2. Lenz, F., in Electron Microcopy in Material Science, (edit. by Valdre, U.), (Academic, London, 1971).
3. cf. Hanszen, K.-J., Adv. opt. Elect. Micr. 4, 1–84 (1971).
4. Hanszen, K.-J., and Trepte, L., Optik, 32, 519–538 (1971).
5. Hanszen, K.-J., and Trepte, L., Optik, 33, 182–198 (1971).