HAL Id: hal-01100647 https://inria.hal.science/hal-01100647 Submitted on 8 Jan 2015 HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplina