  Like any other logical theory, domain descriptions in reasoning about actions
may evolve, and thus need revision methods to adequately accommodate new
information about the behavior of actions. The present work is about changing
action domain descriptions in propositional dynamic logic. Its contribution is
threefold: first we revisit the semantics of action theory contraction that has
been done in previous work, giving more robust operators that express minimal
change based on a notion of distance between Kripke-models. Second we give
algorithms for syntactical action theory contraction and establish their
correctness w.r.t. our semantics. Finally we state postulates for action theory
contraction and assess the behavior of our operators w.r.t. them. Moreover, we
also address the revision counterpart of action theory change, showing that it
benefits from our semantics for contraction.
