Analytic Tableaux for KLM Preferential and Cumulative Logics

We present tableau calculi for some logics of default reasoning, as defined by Kraus, Lehmann and Magidor. We give a tableau proof procedure for preferential and cumulative logics. Our calculi are obtained by introducing suitable modalities to interpret conditional assertions. Moreover, they give a decision procedure for the respective logics and can be used to establish their complexity.