∀ (x : ℕ)
  (f :
    Nat.below (motive := fun x =>
      ∀ (x_1 : ℕ),
        List.Pairwise (Pi.Lex (fun x1 x2 => x1 < x2) fun x x1 x2 => x1 < x2) (List.Nat.antidiagonalTuple x x_1))
      x)
  (x_1 : ℕ), List.Pairwise (Pi.Lex (fun x1 x2 => x1 < x2) fun x x1 x2 => x1 < x2) (List.Nat.antidiagonalTuple x x_1)