Olivier Fourdrinoy Éric Grégoire Bertrand Mazure Lakhdar Sais Reducing hard SAT instances to polynomial ones. 18-23 2007 conf/iri/2007 IRI http://dx.doi.org/10.1109/IRI.2007.4296591 db/conf/iri/iri2007.html#FourdrinoyGMS07