intro v
n : ℕ
i j : Fin n
F : Vector ℕ (n + 1) → ℕ :=
  fun v =>
    ((v.head + v.get j.succ).isEqNat (v.get i.succ)).or (((v.get i.succ).isLtNat (v.get j.succ)).and (v.head.isEqNat 0))
this : Arith₁ F
⊢ ∀ (i_1 : Vector ℕ n), (rfind fun n_1 => Part.some (decide (0 < F (n_1 ::ᵥ i_1)))) = (↑fun v => v.get i - v.get j) i_1
n : ℕ
i j : Fin n
F : Vector ℕ (n + 1) → ℕ :=
  fun v =>
    ((v.head + v.get j.succ).isEqNat (v.get i.succ)).or (((v.get i.succ).isLtNat (v.get j.succ)).and (v.head.isEqNat 0))
this : Arith₁ F
v : Vector ℕ n
⊢ (rfind fun n_1 => Part.some (decide (0 < F (n_1 ::ᵥ v)))) = (↑fun v => v.get i - v.get j) v