@Unpublished{BagnaraHZ04FAC, Author = "R. Bagnara and P. M. Hill and E. Zaffanella", Title = "Not Necessarily Closed Convex Polyhedra and the Double Description Method", Year = 2004, Note = "Submitted for publication. Available at \url{http://www.cs.unipr.it/~bagnara/}", }