Patrick Doherty Witold Lukaszewicz Andrzej Szalas Similarity, Approximations and Vagueness. 541-550 2005 conf/rsfdgrc/2005-1 RSFDGrC (1) http://dx.doi.org/10.1007/11548669_56 db/conf/rsfdgrc/rsfdgrc2005-1.html#DohertyLS05