Defeasible Goals

. In this paper we study defeasible goals in Gabbay's labelled deductive systems. We prove the completeness of a simple and elegant proof theory for the labelled logic of defeasible goals by proving two phasing theorems. 1 Introduction In the usual approaches to planning in AI, a planning agent is provided with a description of some state of aairs, a goal state, and charged with the task of discovering (or performing) some sequence of actions to achieve that goal. Recently several logics for goals (and the closely related desires) have been proposed [4, 3, 12, 2, 14, 13, 8, 6, 15, 16]. We are interested in a logical system that tells us which conditional goals can be derived from a set of conditional goals (the set of premises) called the goal base. In this simple setting { in which we do not consider logical connectives between the conditional goals { reasoning about goals is non-trivial for the following three reasons. Goals can conict. Some students desire to do research and..