∀ {α : Type u_1} (motive : (l₁ l₂ : List α) → l₁.length ≤ l₂.length → Prop) (l₁ l₂ : List α)
  (hle : l₁.length ≤ l₂.length),
  (∀ (x : List α) (hle : [].length ≤ x.length), motive [] x hle) →
    (∀ (head : α) (tail : List α) (hle : (head :: tail).length ≤ [].length), motive (head :: tail) [] hle) →
      (∀ (a : α) (l₁ : List α) (b : α) (l₂ : List α) (hle : (a :: l₁).length ≤ (b :: l₂).length),
          motive (a :: l₁) (b :: l₂) hle) →
        motive l₁ l₂ hle