The law says nothing about computability (nice straw man) but it does say ideas and math are not protected whereas code is. My point is the API declarations at the heart of this case are not protected by law because they are examples of the former. Like a formula, they are ideas that describe what to do, but not exactly how to do it.

If you code GCD in a low-level computer programming language then of course you can claim a copyright on that code, but nobody owns the idea of the Euclidean algorithm.