I didn't say that union types are a key concept in abstract algebra, and I'm not a mathematician by any means, although I vaguely understand that a disjoint uni

I didn't say that union types are a key concept in abstract algebra, and I'm not a mathematician by any means, although I vaguely understand that a disjoint union is a thing in set theory. What I'm saying is that languages that do embrace concepts from abstract algebra, are much more expressive than languages that eschew these concepts (like Java).