English
If nhdsWithin x s sees f1 equal to f, then fderivWithin f1 s x = fderivWithin f s x when x ∈ s.
Русский
Если nhdsWithin x s фиксирует равенство f1 и f, то fderivWithin f1 s x = fderivWithin f s x при x ∈ s.
LaTeX
$$$ (nhdsWithin x s).\\text{EventuallyEq}(f_1,f) \\to x\\in s \\to \\mathrm{fderivWithin}(f_1,s,x) = \\mathrm{fderivWithin}(f,s,x) $$$
Lean4
theorem fderivWithin_congr_mono (h : DifferentiableWithinAt 𝕜 f s x) (hs : EqOn f₁ f t) (hx : f₁ x = f x)
(hxt : UniqueDiffWithinAt 𝕜 t x) (h₁ : t ⊆ s) : fderivWithin 𝕜 f₁ t x = fderivWithin 𝕜 f s x :=
(HasFDerivWithinAt.congr_mono h.hasFDerivWithinAt hs hx h₁).fderivWithin hxt