Preemption Operators

We introduce a family of operators for belief change that aim at making a new piece of information to be preemptive so that any former belief subsuming it is given up. That is, the current belief base is to be altered even in the case that it is logically consistent with the new piece of information. Existing operators for belief revision are inadequate for this purpose because they amount to settheoretic union in a contradiction-free case. We propose a series of postulates for such preemption operators. We show that a preemption operator can be defined as a multiple contraction followed by an expansion, drawing on operators from belief revision.