∀ {α : Sort uA} {β : Sort uB} {φ : Sort uC} {s₁ : Setoid α} {s₂ : Setoid β} (q₁ q₁_1 : Quotient s₁),
  q₁ = q₁_1 →
    ∀ (q₂ q₂_1 : Quotient s₂),
      q₂ = q₂_1 →
        ∀ (f f_1 : α → β → φ) (e_f : f = f_1)
          (c : ∀ (a₁ : α) (b₁ : β) (a₂ : α) (b₂ : β), a₁ ≈ a₂ → b₁ ≈ b₂ → f a₁ b₁ = f a₂ b₂),
          q₁.liftOn₂ q₂ f c = q₁_1.liftOn₂ q₂_1 f_1 ⋯