1. A. Litke, G. Hanson, A. Hofmann, J. Koch, L. Law, M. E. Law, J. Leong, R. Little, R. Madaras, H. Newman, J. M. Paterson, R. Pordes, K. Strauch, G. Tarnopolsky andR. Wilson:Phys. Rev. Lett.,30, 1189 (1973).
2. Reported byB. Richter atIrvine Conference on Lepton Induced Interactions, 1973, to be published.
3. Pointed out byM. Schwartz atIrvine Conference.
4. C. Quigg andJ. D. Jackson: UCRL 18487 (1968, unpublished).
5. SeeJ. M. Jauch andF. Rohrlich:Theory of Photons and Electrons (Reading, Mass., 1955), p. 275–286, for the proof in the analogous case of the selection rules for positronium.