Stefano Bistarelli Fabio Gadducci Javier Larrosa Emma Rollon A Soft Approach to Multi-objective Optimization. 764-768 2008 ICLP http://dx.doi.org/10.1007/978-3-540-89982-2_73 conf/iclp/2008 db/conf/iclp/iclp2008.html#BistarelliGLR08