Copyright (c) 2010-2018 Centre National de la Recherche Scientifique. written by Nathanael Schaeffer (CNRS, ISTerre, Grenoble, France). nathanael.schaeffer@univ-grenoble-alpes.fr This software is governed by the CeCILL license under French law and abiding by the rules of distribution of free software. You can use, modify and/or redistribute the software under the terms of the CeCILL license as circulated by CEA, CNRS and INRIA at the following URL "http://www.cecill.info". The fact that you are presently reading this means that you have had knowledge of the CeCILL license and that you accept its terms.