A Modified Subformula Property for the Modal Logics K5 and K5d
نویسنده
چکیده
The sequent calculus GK5 (GK5D) for the modal propositional logic K5 (K5D) is presented, and it is shown that, every provable sequent Γ → Θ in GK5 (GK5D) has a GK5-proof (GK5D-proof) such that every formula occurring in it is either a subformula of some formulas in Γ, Θ, or the formula 2¬2B or ¬2B, where 2B occurs in the scope of some occurrence of 2 in some formulas of Γ, Θ. Some corollaries including the interpolation property for K5 (K5D) follow from this.
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تاریخ انتشار 2007