match hf with
| .nil =>
  constructor
| .cons (t := t) (ts := ts) lt _ _ =>
  constructor
  . have : h₁.rank + 1 ≤ t.rank := by
      apply Nat.succ_le_of_lt lt
    apply lt_of_le_of_ne this
    rw[hrank_of_cons] at *
    unfold bne at *
    rw[Nat.not_beq_eq_true_eq] at *
    assumption
  . assumption
  . assumption
α : Type u_1
le : α → α → Bool
rx : ℕ
xs : List (BinTree α)
ry : ℕ
ys : List (BinTree α)
h₁ : BinTree α
t₁ : List (BinTree α)
h₂ : BinTree α
t₂ : List (BinTree α)
hxs : IsHeapForest' rx (h₁ :: t₁)
hys : IsHeapForest' ry (h₂ :: t₂)
not_le_le : ∀ (x y : α), le x y = false → le y x = true
h✝³ : h₂.rank ≤ h₁.rank
h✝² : h₁.rank ≤ h₂.rank
heq : h₁.rank = h₂.rank
a✝¹ : rx < h₁.rank
a✝ : IsBinTree h₁
hf : IsHeapForest' h₁.rank t₁
h✝¹ : (h₁.rank + 1 != hRank t₁) = true
h✝ : (h₁.rank + 1 != hRank t₂) = false
⊢ IsHeapForest' (h₁.rank + 1) t₁
no goals