1. Atkinson, D., Johnson, P., Warnock, R.: Commun. math. Phys.28, 133 (1972). References to previous work are given there. See also Ref. 6
2. Atkinson, D., Mahoux, G., Ynduräin, F.: Nucl. Phys. B54, 263 (1973)
3. Schauder's theorem is discussed in, for example, Kantorowitsch, L. V., Akilow, G. V.: Functional analyse in Normierten Räumen (German translation by Berlin: Akademie Verlag 1964)
4. Bart, G., Johnson, P., Warnock, R.: “Continuum Ambiguity in the Construction of preprint, Unitary Analytic Amplitudes from Fixed Energy Scattering Data”, IIT December, 1972
5. Liusternik, L., Sobolev, V.: Elements of Functional Analysis, pp. 138–141. English translation published by New York: F. Ungar, 1961