Francesc Esteva Joan Gispert Lluis Godo Carles Noguera Adding truth-constants to logics of continuous t-norms: Axiomatization and completeness results. 597-618 2007 158 Fuzzy Sets and Systems 6 http://dx.doi.org/10.1016/j.fss.2006.11.010 db/journals/fss/fss158.html#EstevaGGN07