Default Reasoning about Spatial Occupancy

This paper describes a default reasoning problem, analogous to the frame problem, that arises when an attempt is made to construct a logic-based calculus for reasoning about the movement of objects in a real-valued co-ordinate system. A number of potential solutions to this problem are examined. Particular attention is given to the interaction between the default reasoning required by these solutions and that required to overcome the frame problem, especially when the latter demands an “existence of situations” axiom.