1. See, for example, L.I. Schiff, Quantum Mechanics (McGraw-Hill, New York, 1968).
2. L.S. Kisslinger, Phys. Rev. 98, 761 (1955).
3. C.M. Bender, Advanced Mathematical Methods for Scientists and Engineers (McGraw-Hill, New York, 1978) p. 330.
4. A.R. Plastino , Phys. Rev. A 60, 4318 (1999).
5. A. de Souza Dutra , Europhys. Lett. 62, 8 (2003).