1. I. Bialynicki-Birula and J. Mycielski, Ann. Phys. (NY) 100 (1976), 62.
2. H.-D. Doebner and G. A. Goldin, Phys. Lett. A 162 (1992), 397.
3. H.-D. Doebner and G. A. Goldin, in: Annales de Fisica, Monografias, Vol. II, Proceedings of the 17th International Conference on Group Theoretical Methods in Physics, Salamanca, 1992, CIEMAT, Madrid, 1993, 442–445.
4. H.-D. Doebner and G. A. Goldin, in: Proceedings of the First German-Polish Symposium on Particles and Fields, Rydzyna Castle, 1992, World Scientific, Singapore, 1993, 115 ff.
5. H.-D. Doebner and G. A. Goldin, J. Phys. A: Math. Gen. 27 (1994), 1771.