English
If two sets s and t coincide near x, ContDiffWithinAt on s and t are equivalent for a fixed f.
Русский
Если множества s и t совпадают около x, ContDiffWithinAt на s и t равнозначны для заданной f.
LaTeX
$$$ (nhds x).EventuallyEq s t \\Rightarrow ContDiffWithinAt 𝕜 n f s x \\iff ContDiffWithinAt 𝕜 n f t x$$
Lean4
theorem congr (h : ContDiffWithinAt 𝕜 n f s x) (h₁ : ∀ y ∈ s, f₁ y = f y) (hx : f₁ x = f x) :
ContDiffWithinAt 𝕜 n f₁ s x :=
h.congr_of_eventuallyEq (Filter.eventuallyEq_of_mem self_mem_nhdsWithin h₁) hx