TY - JOUR
AU - Wojtylak, Piotr
AB - A projective unifier for a modal formula A, over a modal logic L, is a unifier  for A (i.e. a substitution making A a theorem of L) such that the equivalence of  with the identity map is the consequence of A. Each projective unifier is a most general unifier for A.Let L be a normal modal logic containing S4. We show that every unifiable formula has a projective unifier in L iff L contains S4.3. The syntactic proof is effective. As a corollary, we conclude that all normal modal logics L containing S4.3 are almost structurally complete, i.e. all (structural) admissible rules having unifiable premises are derivable in L. Moreover, L is (hereditarily) structurally complete iff L contains McKinsey axiom M.
TI - Projective unification in modal logic
JO - Logic Journal of the IGPL
DO - 10.1093/jigpal/jzr028
DA - 2012-02-07
UR - https://www.deepdyve.com/lp/oxford-university-press/projective-unification-in-modal-logic-03HmKVo327
SP - 121
EP - 153
VL - 20
IS - 1
DP - DeepDyve
ER -