“…The notions of similarity, equivalence, and indistinguishability relations have been well investigated with set-based approaches (Bittner & Stell, 2003;Chen & Yao, 2006;Hata & Mukaidono, 1999;Keet, 2007a;Mencar et al, 2007;Peters et al, 2002;Skowron & Peters, 2003;Yao, 2004). However, this set-based approach has issues that can be better addressed with mereology proper (Abelló et al, 2006;Bittner & Smith, 2003;Keet, 2008a). The research programme of rough mereology (see, e.g., Polkowski (2006); Polkowski & Semeniuk-Polkowska (2008) for recent results) has, from an ontological (Varzi, 2004;Keet & Artale, 2008) and logical (Pontow & Schubert, 2006) perspective, a comparatively weak mereology component, because it is tightly coupled with the set-based approach and remains close to Lesniewski's pioneering work without considering newer mereological theories.…”