English
For a differentiable function f: 𝕜 → F at x within any set s, the magnitude of the derivative within s equals the operator norm of the corresponding Fréchet derivative. In symbols: ‖derivWithin f s x‖ = ‖fderiv 𝕜 f s x‖.
Русский
Для функции f: 𝕜 → F, дифференцируемой в точке x с учётом множества s, величина производной внутри s равна операторной норме соответствующего ФрÉш derivative: ‖derivWithin f s x‖ = ‖fderiv 𝕜 f s x‖.
LaTeX
$$$\\\\| \\\\operatorname{derivWithin} f s x \\\\| = \\\\| fderiv \\\\ 𝕜 \\\\ f s x \\\\|$$$
Lean4
theorem norm_derivWithin_eq_norm_fderivWithin : ‖derivWithin f s x‖ = ‖fderivWithin 𝕜 f s x‖ := by
simp [← derivWithin_fderivWithin]