English
If h is MF-differentiable within at s and t ⊆ s with equality on t, then the mfderivWithin values are equal.
Русский
Если h дифференцируем внутри s, и t ⊆ s с равенством на t, то значения mfderivWithin равны.
LaTeX
$$$MDifferentiableWithinAt\ I I'\ f\ s\ x\ f' \land t\subseteq s \land (\forall y\in t, f_1(y)=f(y)) \Rightarrow mfderivWithin\ I I'\ f\ t\ x = mfderivWithin\ I I'\ f\ s\ x$$$
Lean4
theorem congr (h : MDifferentiableWithinAt I I' f s x) (ht : ∀ x ∈ s, f₁ x = f x) (hx : f₁ x = f x) :
MDifferentiableWithinAt I I' f₁ s x :=
(HasMFDerivWithinAt.congr_mono h.hasMFDerivWithinAt ht hx (Subset.refl _)).mdifferentiableWithinAt