Vilém Novák Irina Perfilieva Libor Behounek Petr Cintula Formal methods for fuzzy mathematics, approximation and reasoning - Part II. 1003-1004 2009 160 Fuzzy Sets and Systems 8 http://dx.doi.org/10.1016/j.fss.2008.11.009 db/journals/fss/fss160.html#NovakPBC09