Possibilistic and probabilistic logic under coherence: default reasoning and System P.

Some results on coherence in probabilistic and in possibilistic frameworks are presented in order to deal with nonmonotonic reasoning. Moreover, we extend these results to conditional decomposable measures. We deal with entailment and prove that it satisfies the axiomatization of System P by referring to conditional necessities or to specific conditional decomposable measures (which include conditional probability). Finally, we study some aspects concerning a notion of irrelevance.