case cons a₁ as =>
  simp [List.cons_append] at *
  intro has; cases has with | cons ha htail =>
  exact Ascending.cons ha (h_ind htail)
α : Type u
r : α → α → Prop
bs : List α
a a₁ : α
as : List α
h_ind : Ascending r (a₁ :: as ++ bs) → Ascending r (a₁ :: as)
⊢ Ascending r (a :: a₁ :: as ++ bs) → Ascending r (a :: a₁ :: as)
no goals