English
If f is differentiable within at x on s, then exp(f) is differentiable within at x on s.
Русский
Если f дифференцируема внутри множества s в точке x, то exp(f) дифференцируема внутри s в x.
LaTeX
$$$$ \text{DifferentiableWithinAt}_{\mathbb{R}}(f, s, x) \Rightarrow \text{DifferentiableWithinAt}_{\mathbb{R}}(\lambda y. \exp(f(y)), s, x) $$$$
Lean4
theorem exp (hf : DifferentiableWithinAt ℝ f s x) : DifferentiableWithinAt ℝ (fun x => Real.exp (f x)) s x :=
hf.hasFDerivWithinAt.exp.differentiableWithinAt