Copyright (C) 2000-2006, HELM Team. Matita is part of HELM, an Hypertextual, Electronic Library of Mathematics, developed at the Computer Science Department, University of Bologna, Italy. HELM is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. HELM is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with HELM; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. For details, see the HELM World-Wide-Web page, http://helm.cs.unibo.it/