∀ {𝕜 : Type u_1} {E : Type u_2} {M : Type u_3} {H : Type u_4} [inst : NontriviallyNormedField 𝕜]
  [inst_1 : NormedAddCommGroup E] [inst_2 : NormedSpace 𝕜 E] [inst_3 : TopologicalSpace H] [inst_4 : TopologicalSpace M]
  (f : OpenPartialHomeomorph M H) {I : ModelWithCorners 𝕜 E H} {y : M},
  y ∈ f.source → nhdsWithin (↑(f.extend I) y) (f.extend I).target = nhdsWithin (↑(f.extend I) y) (Set.range ↑I)