It is pointless if you make it an ontological exercise. If you make it a question of substitutability (as your link does), then I agree that you're doing it th

It is pointless if you make it an ontological exercise. If you make it a question of substitutability (as your link does), then I agree that you're doing it the right way. The question shouldn't be: "is a Square a special kind of Rectangle, in a pure/platonic/logical sense?" The question should be "can a Square be treated as if it were a Rectangle." The answer to the second question could depend on the program and what it wants to do! The first is a rathole that accomplishes nothing.