1. The first discussion of pion double charge exchange appears to have been between S. D. Drell, H. J. Lipkin and A. deShalit in 1961–2. One of the first written discussions was by T. E. O. Ericson, Proceedings of 1963 International Conference on High Energy Physics and Nuclear Structure, CERN Report 63–28, July 1, 1963.
2. J. D. Anderson and C. Wong, Phys. Rev. Lett. 7 (1961) 250. See also Phys. Rev. Lett. 8 (1962) 442
3. J. D. Anderson, C. Wong and J. W. McClure, Phys. Rev. 126 (1962) 2170.
4. See for instance: I. V. Falomkin, M. M. Kulyukin, V. I. Lyashenko, G. B. Pontecorvo, Y. A. Shcherbakov, M. Albu, T. Angelescu, A. Mihui, F. Nichitiu, R. Garfagnini, and J. Piragino, “Elastic Scattering of π+ and π-” Mesons on 3He at 154 MeV, Nuovo Cimento 24, 93 (1974).
5. See for instance: E. Pedroni, K. Galathuler, J. Arvieux, J. Domingo, P. Gretillat, W. Hirt, Q. Ingram, J. Piffaretti, P. Schwaller, N. Tanner, C. Wilkin, Paper Ell.