Belief Change - Nuclear Contraction Operator Research

The theory of belief revision is an important branch in the research of artificial intelligence. Many researchers have discussed about it, and put forward lots of methods according to different requirements in different applicable areas, the most representative of which is the AGM theory. On the basis of the AGM theory and kernel contraction, this thesis mainly discusses the theory of belief contraction in which new information is a general set of sentences. The main work can be divided into the following parts:(1) The thesis gives the construction of package-kernel contraction and its postulates and proof of corresponding representation theorem.(2) It gives representation theorems of saturated package-kernel contraction and smooth package-kernel contraction, and proves that the two contraction operations coincide with each other. It discusses the relation between smooth package-kernel contraction and package contraction basing on partial meet contraction.(3) It constructs the choice-kernel contraction and gives corresponding postulates and representation theorem, and discusses sub kernel contraction and its representation theorem.