International Journal of Modern Physics A: Particles & Fields; Gravitation; Cosmology; Nuclear Physics, 1997, v. 12, n. 12, p. 2293, doi. 10.1142/S0217751X9700133X
International Journal of Modern Physics A: Particles & Fields; Gravitation; Cosmology; Nuclear Physics, 1997, v. 12, n. 12, p. 2135, doi. 10.1142/S0217751X97001328