Institution: | 1 System Engineering and Computer Science Program - UFRJ - Mailbox 68511, zipcode 21945970 Rio de Janeiro, Brazil. E-mail: vaniac{at}cos.ufrj.br, 2 System Engineering and Computer Science Program and Institute of Mathematics - UFRJ - Mailbox 68511, zipcode 21945970 Rio de Janeiro, Brazil. E-mail: mario{at}cos.ufrj.br |