Institution: | 1 CLC, Dep. Matemática, IST, Av. Rovisco Pais, 1049-001, Lisbon, Portugal. E-mail: pmat{at}math.ist.utl.pt, acs{at}math.ist.utl.pt, css{at}math.ist.utl.pt 2 ETH Zentrum, IFW C43.1 Haldeneggsteig 4 CH-8092 Zürich, Switzerland. E-mail: vigano{at}inf.ethz.ch |