English
If hq : ∀ h, q h ↔ q' h and hp : p ↔ p', then (∀ h, q h) ↔ ∀ h: p', q'(hp.2 h).
Русский
Если hq : ∀ h, q h ↔ q' h и hp : p ↔ p', то (∀ h, q h) ↔ ∀ h: p', q'(hp.2 h).
LaTeX
$$$(\forall h, q(h)) \iff (\forall h : p', q'(hp.2(h)))$$$
Lean4
theorem forall_prop_congr {p p' : Prop} {q q' : p → Prop} (hq : ∀ h, q h ↔ q' h) (hp : p ↔ p') :
(∀ h, q h) ↔ ∀ h : p', q' (hp.2 h) :=
⟨fun h1 h2 ↦ (hq _).1 (h1 (hp.2 h2)), fun h1 h2 ↦ (hq _).2 (h1 (hp.1 h2))⟩