KERML — Type union, intersection, difference semantics

Type unioning, intersecting, and differing are described as

Unioning, intersecting, and differencing are relationships between an owning type and a set of other types.
1. Unioning specifies that the owning type classifies everything that is classified by any of the unioned types.
2. Intersecting specifies that the owning type classifies everything that is classified by all of the intersecting types.
3. Differencing specifies that the owning type classifies everything that is classified by the first of the differenced types but not by any of the remaining types.

but this semantics is not math/modeled.