FRAMES IN THE SPACE OF SITUATIONS

Some of the formalizations discussed in recent work on action and change use variables for propositional fluents. The authors do not specify whether these variables are meant to range over the set of all propositional fluents or over some part of this set. We show that this seemingly minor detail affects the acceptability of some postulates proposed in the literature. We argue that it is important to distinguish between assertions about arbitrary fluents and assertions about the fluents that belong to a "frame" in the space of situations. © 1990.