Before revision: The AGM postulates for revision are: Closure: is a belief set (i.e., a deductively closed set of formulae); Success: Inclusion: Vacuity: is inconsistent only if is inconsistent Extensionality: (see logical equivalence) A revision operator that satisfies all eight postulates is the full meet revision, in which is equal to if consistent, and to the deductive closure of otherwise.
After revision: Consistency:Superexpansion: Subexpansion:The AGM postulates for revision are: Closure: is a belief set (i.e., a deductively closed set of formulae); Success: Inclusion: Vacuity: is inconsistent only if is inconsistent Extensionality: (see logical equivalence) A revision operator that satisfies all eight postulates is the full meet revision, in which is equal to if consistent, and to the deductive closure of otherwise.