1. E. Wigner andJ. Neumann:Annals of Math.,59, 418 (1954).
2. D. S. Carter:Thesis, Princeton;N. Khuri:Phys. Rev. 107 1148 (1957). We have had no opportunity of examining directlyCarter’s work and we know of his result only throughKhuri’s paper.
3. I. M. Gel’fand andLevitan:Amer. Math. Soc. Trans., Sec. 2.1.250 (1955).
4. R. Jost andW. Kohn:Math. Phys. Medd.,27, (9) (1953).
5. L. D. Faddeev:Soviet Phys. Dokl. Transl.,3, 747 (1959).