A Modal Logic for Pawlak's Approximation Spaces with Rough Cardinality n

  • Authors:
  • Philippe Balbiani;Petar Iliev;Dimiter Vakarelov

  • Affiliations:
  • Universiteacute/ Paul Sabatier, Institut de recherche en informatique de Toulouse, 31062 Toulouse Cedex 9, France. E-mail: balbiani@irit.fr;Sofia University, Faculty of Mathematics and Computer Science, blvd James Bouchier 5, 1126 Sofia, Bulgaria. E-mails: petar.iliev@gmail.com, dvak@fmi.univ-sofia.bg;Sofia University, Faculty of Mathematics and Computer Science, blvd James Bouchier 5, 1126 Sofia, Bulgaria. E-mails: petar.iliev@gmail.com, dvak@fmi.univ-sofia.bg

  • Venue:
  • Fundamenta Informaticae
  • Year:
  • 2008

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Abstract

The natural modal logic corresponding to Pawlak's approximationspaces is S5, based on the box modality [R]A (and the diamondmodality )R*A=¬[R]¬A), where R is the correspondingindiscernibility relation of the approximation space S=(W,R).However the expressive power of S5 is too weak and, for instance,we cannot express that the space S has exactly n equivalenceclasses (we say that S is roughly-finite and n is therough cardinality of S). For this reason we extend the modallogic S5 with a new box modality [S]A, where S is the complement ofR i.e. the discernibility relation of W. We propose acomplete axiomatization, in this new language, of the logicROUGHn corresponding to the class of approximationspaces with rough cardinality n. We prove that the satisfiabilityproblem for ROUGHn is NP-complete.