“…In the late 1980s and early 1990s various direct resolution methods for modal logics have been investigated [1,10,33,46,59,61,72,79,126,139,140]. According to [139] a resolution method for a logic L is determined by specifying (i) a class of formulae called clauses, (ii) a reduction method which allows us to transform any formula of L into a finite set of clauses, (iii) a calculus consisting of a set of resolution rules for deriving clauses (and possibly redundancy elimination and simplification rules), and (iv) a derivation process which starts from an initial set of clauses and constructs a sequence of derivable clauses.…”