Bernard De Baets Francesc Esteva János C. Fodor Lluis Godo Systems of ordinal fuzzy logic with application to preference modelling. 47-50 1999 EUSFLAT-ESTYLF Joint Conf. http://www.eusflat.org/publications/proceedings/EUSFLAT-ESTYLF_1999/papers/047-Fodor-especial.pdf conf/eusflat/1999 db/conf/eusflat/eusflat1999.html#BaetsEFG99