Copyright c 2003 Davide Rocchesso. Permission is granted to copy,
distribute and/or modify this document under the terms of the GNU
Free Documentation License, Version 1.2 or any later version pub-
lished by the Free Software Foundation; with no Invariant Sections,
no Front-Cover Texts, and no Back-Cover Texts. A copy of the li-
cense is included in the appendix entitled "GNU Free Documentation
License".