Localización:Symmetries in quantum mechanics and quantum optics: proceedings of the First International Workshop. Burgos (Spain), 21-24 September 1998 / Ángel Ballesteros Castañeda (ed. lit.) , Francisco J. Herranz Zorrilla (ed. lit.) , Javier Negro Vadillo (ed. lit.) , Luis Miguel Nieto (ed. lit.), Carmen María Pereña Fernández (ed. lit.), 1999, ISBN 84-95211-08-4, págs. 17-32