Vilém Novák Irina Perfilieva Libor Behounek Petr Cintula Formal methods for fuzzy mathematics, approximation and reasoning - Part I. 1727-1728 2008 159 Fuzzy Sets and Systems 14 http://dx.doi.org/10.1016/j.fss.2008.01.004 db/journals/fss/fss159.html#NovakPBC08