rintro x z ys ⟨x_is_head, z_is_last, steprel⟩
α : Type u_1
r : α → α → Prop
n : ℕ
IH :
  ∀ (x z : α) (ys : Vector α n.succ),
    (x = ys.head ∧ z = ys.last ∧ ∀ (i : Fin n), r (ys.get i.castSucc) (ys.get i.succ)) → Relation.ReflTransGen r x z
⊢ ∀ (x z : α) (ys : Vector α (n + 1).succ),
    (x = ys.head ∧ z = ys.last ∧ ∀ (i : Fin (n + 1)), r (ys.get i.castSucc) (ys.get i.succ)) →
      Relation.ReflTransGen r x z
case intro.intro
α : Type u_1
r : α → α → Prop
n : ℕ
IH :
  ∀ (x z : α) (ys : Vector α n.succ),
    (x = ys.head ∧ z = ys.last ∧ ∀ (i : Fin n), r (ys.get i.castSucc) (ys.get i.succ)) → Relation.ReflTransGen r x z
x z : α
ys : Vector α (n + 1).succ
x_is_head : x = ys.head
z_is_last : z = ys.last
steprel : ∀ (i : Fin (n + 1)), r (ys.get i.castSucc) (ys.get i.succ)
⊢ Relation.ReflTransGen r x z