A subtle differentiable function is the scalar product,
for a vector space $V$.
Derivative
By Liebniz rule, the total derivative is
Gradient
Note that depends on the vector space structure on $(\mathbb{R}, V)$. For a vector $w$ in $V$, note that we can write
By definition of gradient (as adjoint derivative), we have
Code
We need an additional implicit structure with combinators:
1 2 3 
