. next hd tl ih =>
  simp only [List.foldl]
  intro h0
  let update_res := insertUnit (rupUnits, assignments, b) hd
  have update_res_size : update_res.2.1.size = n := by rw [insertUnit_preserves_size]; exact assignments_size
  have h := insertUnit_preserves_invariant assignments0 assignments0_size rupUnits assignments assignments_size b hd h0
  exact ih update_res.1 update_res.2.1 update_res_size update_res.2.2 h
case cons
n : Nat
assignments0 : Array Assignment
assignments0_size : assignments0.size = n
head✝ : Literal (PosFin n)
tail✝ : List (Literal (PosFin n))
tail_ih✝ :
  ∀ (rupUnits : Array (Literal (PosFin n))) (assignments : Array Assignment) (assignments_size : assignments.size = n)
    (b : Bool),
    insertUnit_invariant assignments0 assignments0_size rupUnits assignments assignments_size →
      let update_res := List.foldl insertUnit (rupUnits, assignments, b) tail✝;
      let_fun update_res_size := ⋯;
      insertUnit_invariant assignments0 assignments0_size update_res.fst update_res.snd.fst update_res_size
rupUnits : Array (Literal (PosFin n))
assignments : Array Assignment
assignments_size : assignments.size = n
b : Bool
⊢ insertUnit_invariant assignments0 assignments0_size rupUnits assignments assignments_size →
    let update_res := List.foldl insertUnit (rupUnits, assignments, b) (head✝ :: tail✝);
    let_fun update_res_size := ⋯;
    insertUnit_invariant assignments0 assignments0_size update_res.fst update_res.snd.fst update_res_size
no goals