1. W. Sandhas, The Three-Body Problems, in Elementary Particle Physics, ed.: P. Urban (Acta Physica Austriaca, Suppl. IX, 57 (1972)).
2. L. D. Faddeev, Mathematical Aspects of the Three-Body Problem in the Quantum Scattering Theory (English translation: Israel Program for Scientific Translation, Jerusalem, 1965 ).
3. Compare also: E. 0. Alt, P. Grassberger, W. Sandhas, JIRN, E4–6688, Dubna, 1972. See furthermore p. 299 of Few Particle Problems, ed.: I. Slaus et al., North-Holland, 1972 (Proceedings of the Los Angeles Conference 1972 ).
4. The definition of 2(+) by a time limit is given in Eq. (2.9) of Ref. 1.
5. Without going into any details we recall that in the Heisenberg picture the relevant operators have to be sandwiched between eigenstates of the total Hamiltonian. These, however, are in our case the scattering states