match hf with
| .nil => 
  constructor
| .cons (t := t) (ts := ts) lt _ _ =>
  constructor
  . rw[hrank_of_cons] at *
    rename_i neq
    unfold bne at neq
    rw[Nat.not_beq_eq_true_eq] at neq
    have : h₁.rank + 1 ≤  t.rank := by
      apply Nat.succ_le_of_lt lt
    apply lt_of_le_of_ne <;> assumption
  repeat assumption
case a.cons
α : Type u_1
le : α → α → Bool
r : ℕ
xs ys : List (BinTree α)
h₁ : BinTree α
t₁ : List (BinTree α)
h₂ : BinTree α
t₂ : List (BinTree α)
ht₂ : IsHeapForest' r (h₂ :: t₂)
h✝³ : (h₁.rank + 1 != hRank t₁) = true
not_le_le : ∀ (x y : α), le x y = false → le y x = true
h✝² : h₂.rank ≤ h₁.rank
h✝¹ : h₁.rank ≤ h₂.rank
h✝ : (h₁.rank + 1 != hRank t₂) = false
heq : h₁.rank = h₂.rank
a✝¹ : IsBinTree h₁
a✝ : r < h₁.rank
hf : IsHeapForest' h₁.rank t₁
⊢ IsHeapForest' (h₁.rank + 1) t₁
no goals