Affiliation: | 1. Dipartimento di Matematica e Applicazioni per l''Architettura, Università di Firenze, Piazza Ghiberti 27, 50122 Firenze, Italy;2. Department of Mathematics, Ohio State University, 231 W 18th Avenue, Columbus, OH 43210, USA;3. Department of Mathematical Sciences, M&O Building, University of Liverpool, Liverpool L69 3BX, UK;4. Department of Mathematics, Linköping University, SE-581 83 Linköping, Sweden |