Revising Partially Ordered Beliefs
  This paper deals with the revision of partially ordered beliefs. It proposes
a semantic representation of epistemic states by partial pre-orders on
interpretations and a syntactic representation by partially ordered belief
bases. Two revision operations, the revision stemming from the history of
observations and the possibilistic revision, defined when the epistemic state
is represented by a total pre-order, are generalized, at a semantic level, to
the case of a partial pre-order on interpretations, and at a syntactic level,
to the case of a partially ordered belief base. The equivalence between the two
representations is shown for the two revision operations.
