1. Cai, Y.Q., Papini, G., Class. Quantum Grav., 6, 407 (1989)
2. See also: Papini, G., in Advances in the Interplay Between Quantum and Gravity Physics, P.G. Bergmann and V. de Sabbata (eds.), Kluwer Academic Publishers, pp. 317–338 (2002)
3. Chiao, Raymond Y., arXiv: gr-qc/0211078 v4 22 Jan 2003
4. See, for instance: Varma, C.M., Theoretical Survey of HFS, Proc. of the Adriatrico Research Conference on Heavy Fermion Systems, I.C.T.P., Trieste, 1986
5. Cai, Y.Q., Papini, G., Modern Physics Letters A, 4, 1143 (1989);