I'd like to suggest that the definitions of equal, subsumes, specialises and disjoint are made more precise.

Specifically, equal should be defined as being symmetric, reflexive, and transitive. subsumes and specialises should both be defined as reflexive and transitive, and disjoint should be defined as symmetric and transitive.

I would also suggest that equal be defined as being equal to both subsumes and specialises. That is a statement that A equal B is the same as the two statements A subsumes B and A specialises B.

The justification for the above is that these codes are all defined in terms of 'is-a' and thus should satisfy the same constraints.

I'd also be interested in a clarification of A subsumes B also implying that B specialises A.