[brabel]

These types are equivalent if you consider a value of both of these types have the exact same read operations. Calling `get(String)` will return `String | int` in both cases. You're right that you could build a value of one of these types that does NOT conform to the union, however. I am not sure what's the technical name for what I am trying to say... are they "covariantly equivalent"???

EDIT: ok, I just wanted to say that one type, `Map<String, String | int>`, is a supertype of `Map<String, int> | Map<String, String>`, so if a function accepts the former, it also accepts the latter. They're not equivalent but you can substitute one for the other (one way only) and still perform the same operations (always assuming read-only types, if you introduce mutation everything becomes horrible).

I was trying to emphasize how having type "combinations" ends up causing the type system to become undecidable as you end up with infinite combinations possible, but as I haven't really gone too deeply into why, I am having trouble to articulate the argument.