English
For any x and an equivalence e: Option α ≃ Option β, if there exists x' with e(some x) = some x', then some (removeNone_aux e x) = e (some x).
Русский
Для любого x и эвалюации e: Option α ≃ Option β, если существует x' такое, что e(Some x) = Some x', тогда Some (removeNone_aux e x) = e(Some x).
LaTeX
$$$\\forall x\\,\\exists x'\\: e(\\text{Some } x)=\\text{Some } x' \\Rightarrow \\text{Some}(\\text{removeNone_aux } e\, x)= e(\\text{Some } x).$$$
Lean4
theorem removeNone_aux_some {x : α} (h : ∃ x', e (some x) = some x') : some (removeNone_aux e x) = e (some x) := by
simp [removeNone_aux, Option.isSome_iff_exists.mpr h]