English
If y ∈ connectedComponentIn F x, then connectedComponentIn F x = connectedComponentIn F y.
Русский
Если y ∈ connectedComponentIn F x, то connectedComponentIn F x = connectedComponentIn F y.
LaTeX
$$$y \in connectedComponentIn F x \Rightarrow connectedComponentIn F x = connectedComponentIn F y$$$
Lean4
theorem connectedComponentIn_eq {x y : α} {F : Set α} (h : y ∈ connectedComponentIn F x) :
connectedComponentIn F x = connectedComponentIn F y :=
by
have hx : x ∈ F := connectedComponentIn_nonempty_iff.mp ⟨y, h⟩
simp_rw [connectedComponentIn_eq_image hx] at h ⊢
obtain ⟨⟨y, hy⟩, h2y, rfl⟩ := h
simp_rw [connectedComponentIn_eq_image hy, connectedComponent_eq h2y]