1. L. de la Peña, in Stochastic Processes Applied to Physics and Other Related Fields, B. Gómez et al., eds. (World Scientific, Singapore, 1983).
2. T.W. Marshall and E. Santos, in Problems in Quantum Physics: Gdansk '87, L. Kostro et al., eds. (World Scientific, Singapore, 1988)
3. A. V. Barranco, S.A. Brunini and H.M. França, Phys. Rev. A39, 5492 (1989)
4. A.M. Cetto and L. de la Peña, Found. Phys. 19, 419 (1989)
5. A. Rueda, Space Science Rev. 53, 223 (1990); D.C. Cole, Found. Phys. 20, 225 (1990).