Noelia Barreira Manuel G. Penedo Cástor Mariño F. M. Ansia Topological Active Volumes. 337-344 http://dx.doi.org/10.1007/978-3-540-45179-2_42 2003 conf/caip/2003 CAIP db/conf/caip/caip2003.html#BarreiraPMA03