Acknowledgements:

This document was conceived as a reprint collection by C. Lee Giles, whose contributions to it have been crucial; my sincerest thanks go to him. This document has also benefited enormously from comments by Rafael C. Carrasco, Juan Antonio Pérez Ortiz and Asun Castaño and from technical help by Ana Isabel Guijarro, all of whom I thank. Partial support through grant TIC97-0941 of the Spanish Comisión Ministerial de Ciencia y Tecnología is also acknowledged.

Mikel L. Forcada
January 2002