That's a great answer thanks. So (untagged) Union-type of Haskell really (almost) means INTERSECTION. But it is not an intersection in set-theoretic sense if

That's a great answer thanks. So (untagged) Union-type of Haskell really (almost) means INTERSECTION. But it is not an intersection in set-theoretic sense if we think of the values as elements of the sets, because it allows values of both types, but you can only use an intersection of the APIs they provide.