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Research Report CS-RR-168

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Ian P. Gent, A Sequent System for Lewis's Counterfactual Logic VC (November 1, 1990).

Abstract

This report presents a technical result concerning practical proof systems for counterfactual (also known as conditional) logics. In a 1983 paper, HCM de Swart gave sequent based proof systems for two counterfactual logics: Stanlaker's VCS and Lewis's VC. In this report I demonstrate that de Swart's system for VC is incorrect by giving a counterexample. This counterexample does not effect de Swart's system for VCS. Then I give a new sequent based proof system for VC together with soundness and completeness proofs. The system I give is closely modelled on de Swart's/

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I.P. Gent, "A Sequent- or Tableau-Style System for Lewis's Counterfactual Logic VC", Notre Dame Journal of Formal Logic 33 (1992)

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