match hf with
| .nil =>
  constructor
| .cons (t := t) (ts := ts) lt _ _ =>
  rename_i neq
  rw[rank_combine heq, hrank_of_cons] at *
  unfold bne at neq
  rw[Nat.not_beq_eq_true_eq] at neq
  have : u.rank + 1 ≤ t.rank := by
    apply Nat.succ_le_of_lt lt
  constructor
  . apply lt_of_le_of_ne <;> assumption
  . assumption
  . assumption
case a.cons.cons
α : Type u_1
le : α → α → Bool
not_le_le : ∀ (x y : α), ¬le x y = true → le y x = true
r : ℕ
u : BinTree α
y : List (BinTree α)
c : BinTree α
z : List (BinTree α)
heq : u.rank = c.rank
h✝³ : ¬u.rank < c.rank
h✝² : ¬c.rank < u.rank
h✝¹ : ((combine le u c).rank != hRank y) = true
h✝ : ¬((combine le u c).rank != hRank z) = true
a✝⁴ : IsBinTree u
a✝³ : r < u.rank
hf : IsHeapForest' u.rank y
a✝² : IsBinTree c
a✝¹ : r < c.rank
a✝ : IsHeapForest' c.rank z
⊢ IsHeapForest' (combine le u c).rank y
no goals