> The basic idea is to have an expressive programming language where all constructs are differentiable. Since the composition of diffeomorphisms is a diffeomorp

> The basic idea is to have an expressive programming language where all constructs are differentiable. Since the composition of diffeomorphisms is a diffeomorphism, (...) No. It has nothing to do with diffeomorphisms (which are necessarily between spaces of the same dimension), but with piecewise differentiable functions.