cases h₁:destruct y
case h₀
C : Container
x✝ : M C
R : M C → M C → Prop := fun x y => x = construct (destruct y)
x y : M C
h₀✝ : R x y
h₀ : destruct x = destruct (construct (destruct 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)
case h₀.mk
C : Container
x✝ : M C
R : M C → M C → Prop := fun x y => x = construct (destruct y)
x y : M C
h₀✝ : R x y
h₀ : destruct x = destruct (construct (destruct y))
fst✝ : C.A
snd✝ : B C fst✝ → M C
h₁ : destruct y = { fst := fst✝, snd := snd✝ }
⊢ ∃ node k₁ k₂,
    destruct x = { fst := node, snd := k₁ } ∧
      { fst := fst✝, snd := snd✝ } = { fst := node, snd := k₂ } ∧ ∀ (i : B C node), R (k₁ i) (k₂ i)