Eric B> ! avoid 3 Dim because unstable ... Four is perfect, unless not "commutative" ... For "dimensions", infinity is quite too much For any specific application, it's usually best to use whatever is appropriate. And I agree that most people who use an ontology never think about or worry about proofs in any dimension. But please read the article I cited. It shows that the general case (infinity) includes all the special cases as subtypes. Furthermore, it also shows that proofs for the general case (infinity) are often simpler than proofs for any of the special cases. This fact is important for the people who are defining general principles for ontology. The people who just work on specific problems never need to worry about the proofs. But they do need assurance that the people who define the general case know what they're doing. John