The problem is really that you're using the wrong equality type here. You get the right semantics if you use `= : A -> A -> Bool` and then apply it to a `Maybe

The problem is really that you're using the wrong equality type here. You get the right semantics if you use `= : A -> A -> Bool` and then apply it to a `Maybe A` and a `Maybe A` by lifting it: you end up with `Nothing` if either input was `Nothing`, and `Just answer` if both were known.