587.lean:13:2: proof state
A B : Type₁,
s : setoid A,
f : A → B,
c : ∀ (a₁ a₂ : A), a₁ ≈ a₂ → f a₁ = f a₂,
a : A,
g h : B → B,
gh : g = h
⊢ g (f a) = h (f a)