1. G. F. Chew andS. Mandelstam:Phys. Rev.,119, 467 (1960).
2. For a complete list of references seeG. F. Chew:Double dispersion relations and unitarity as the basis for a dynamical theory of strong interactions, published in the bookDispersion Relations edited byG. E. Screaton (Edinburgh, 1961).
3. For a more detailed discussion of the Green’s function of a non-hermitian operator seeP. M. Morse andH. Feshbach:Methods of Theoretical Physics (New York, 1953), pp. 884–886.
4. R. E, Cutkoskt:Journ. Math. Phys.,1, 429 (1960).
5. K. A. Ter-Martirosyan:Sov. Phys. JETP,12, 575 (1961); see alsoNucl. Phys.,25, 353 (1961).