[kcl]

Calculus in Chinese is still calculus. The sphere is smooth, the cube is non-smooth. That's all it takes.

[photon137]

Yes, but what is a non-differentiable curve if you and I don't even have the same definition of a curve? What about a curve which is differentiable in one coordinate system but not so in another?

EDIT: My point is - mathematics is axiomatic in its very basis - the axioms have to be agreed upon by people who agree upon a conclusion derived from those axioms.