English
If f has MDifferentiableAt at x with derivative f', and f1 equals f near x, then f1 has MDifferentiableAt at x with the same derivative.
Русский
Если f дифференцируемо в точке x с дериватом f', и f1 близко к f near x, то f1 дифференцируемо в x с тем же дериватом.
LaTeX
$$$MDifferentiableAt I I' f x \land f_1 =^\! [\mathcal{N} x] f \Rightarrow MDifferentiableAt I I' f_1 x$$$
Lean4
theorem mdifferentiableOn_congr (h₁ : ∀ y ∈ s, f₁ y = f y) : MDifferentiableOn I I' f₁ s ↔ MDifferentiableOn I I' f s :=
differentiableWithinAt_localInvariantProp.liftPropOn_congr_iff h₁