1. H. W. Fowler, Modern English Usage, Clarendon Press Oxford.
2. R. Dolen, D. Horn and C. Schmid, Phys. Rev. 166, 1768 (1968).
3. M. Jacob, VIII. Internationale Universitätswochen für Kernphysik, P. Urban, Editor.
4. D. Horn, ibid.
5. H. J. Lipkin, J. D. Jackson, M. Jacob, Proceedings of the 1969 Lund Conference on Elementary Particles.