A general framework for the logic of theory change.
Krister Segerberg · Bulletin of the Section of Logic · 1996
Dynamic doxastic logic concerns an agent who inhabits a world and is able to form theories about it. In particular there are three types of doxastic action of which he is capable: expanding his beliefs by accepting a proposition φ without modifying the resulting set of beliefs; revising his beliefs by accepting a proposition φ and modifying the resulting set of beliefs; and contracting his beliefs by giving up a proposition φ and modifying the resulting set of beliefs. We use de Rijke’s symbolism +φ for expansion by φ, ∗φ for revision by φ, and −φ for contraction by φ.