1. R.J. Eden: Reviews of Modern Physics 43, 15 (1971)
2. M.B. Einhorn and R. Blankenbecler: Annals of Physics 67, 480, 1971.
3. T. Kinoshita: Lectures at Boulder Summer School (1960).
4. A. Martin: Scattering Theory: Unitarity, Analyticity and Crossing (Springer Verlag, Berlin, 1969).
5. S.M. Roy: High Energy Theorems (Saclay preprint to be published in Physics Reports 1972).