English
The derivative of the update map at i equals the unit vector Pi.single i (1).
Русский
Производная функции обновления в позиции i равна единичному вектору.
LaTeX
$$$deriv\\left(\\text{Function.update } x\\, i\\right)\\; y = \\Pi.single i (1 : 𝕜)$$$
Lean4
theorem deriv_clm_apply (hc : DifferentiableAt 𝕜 c x) (hu : DifferentiableAt 𝕜 u x) :
deriv (fun y => (c y) (u y)) x = deriv c x (u x) + c x (deriv u x) :=
(hc.hasDerivAt.clm_apply hu.hasDerivAt).deriv