1. G. F. Chew: UCRL-9289, The Edinburgh lecture notes:Dispersion Relations, ed. Screaton; The Les Houches Lecture Notes:Dispersion Relations and Elementary Particles, ed. De Witt and Omnés.
2. S. S. Schweber:Relativtstic Quantum Field Theory, p. 505. This book is after-wards referred to as Schweber;F. Coester:Phys. Rev.,89, 619 (1953).
3. R. E. Cutkosky:Journ. Math. Phys.,1, 429 (1960);Phys. Rev. Lett.,4, 624 (1960);J. C. Polkinghorne:Nuovo Cimento,23, 360 (1962);K. Blankenbecler:Phys. Rev.,122, 983 (1961).
4. S. Mandelstam:Phys. Rev.,112, 1344 (1958).
5. R. J. Eden:Lectures on the use of perturbation methods in dispersion theory, Mariland Report no. 211;J. M. Jauch andF. Rohrlich:The Theory of Photons and Electrons (Cambridge, Mass., 1955) Appendix A.5.