Logical Foundations for Cognitive Agents

It is a pleasure and an honor to be able to present this collection of papers to Ray Reiter on the occasion of his 60th birthday. To say that Ray's research has had a deep impact on the field of Artificial Intel­ ligence is a considerable understatement. Better to say that anyone thinking of do­ ing work in areas like deductive databases, default reasoning, diagnosis, reasoning about action, and others should realize that they are likely to end up proving corol­ laries to Ray's theorems. Sometim