1. von Arb H.P. et al., (1984): Phys. Lett. 136 B, 232.
2. von Arb H.P. et al., (1986): Proceedings of the Workshop on Fundamental Muon Physics: Atoms, Nuclei and Particles, ed. C.M. Hoffman, V.W. Hughes and M. Leon, LA-10714-C, p. 103.
3. Badertscher A. et al., (1985): Atomic Physics 9, ed by R.S. van Dyck, Jr. and E.N. Fortson, (World Scientific) p. 83.
4. Baracci L. and Zavattini E. (1990): Phys. Rev. A 41 2352.
5. Berkeland D.J., Hinds E.A. and Boshier M.G. (1995): Phys. Rev. Lett. 75, 2470.