Affiliation: | (1) Department of Computer Science IME-USP, University of São Paulo, Rua do Matão 1010, Cidade Universitária, 05508-090 São Paulo SP, Brazil;(2) Institute of Mathematics, University of Novi Sad, Trg Dositeja Obradovia 4, 21000 Novi Sad Yugoslavia;(3) Department of Applied Mathematics, IMECC-UNICAMP, University of Campinas, CP 6065, 13081-970 Campinas SP, Brazil |