have h₃ := y.node_thm n
C : Container
R : M C → M C → Prop
h₀ :
  ∀ (x y : M C),
    R x y →
      ∃ node k₁ k₂,
        destruct x = { fst := node, snd := k₁ } ∧
          destruct y = { fst := node, snd := k₂ } ∧ ∀ (i : B C node), R (k₁ i) (k₂ i)
n : Nat
h : ∀ (x y : M C), R x y → approx x n = approx y n
x y : M C
h₁ : R x y
h₂ : Approx.node (approx x (Nat.succ n)) = node x
⊢ approx x (Nat.succ n) = approx y (Nat.succ n)
C : Container
R : M C → M C → Prop
h₀ :
  ∀ (x y : M C),
    R x y →
      ∃ node k₁ k₂,
        destruct x = { fst := node, snd := k₁ } ∧
          destruct y = { fst := node, snd := k₂ } ∧ ∀ (i : B C node), R (k₁ i) (k₂ i)
n : Nat
h : ∀ (x y : M C), R x y → approx x n = approx y n
x y : M C
h₁ : R x y
h₂ : Approx.node (approx x (Nat.succ n)) = node x
h₃ : Approx.node (approx y (Nat.succ n)) = node y
⊢ approx x (Nat.succ n) = approx y (Nat.succ n)