∀ {α : Type u} (r : α → α → Prop) [Std.Trichotomous r] (x : List α)
  (f : List.below (motive := fun x => ∀ (x_1 : List α), ¬List.Lex r x x_1 → ¬List.Lex r x_1 x → x = x_1) x)
  (x_1 : List α), ¬List.Lex r x x_1 → ¬List.Lex r x_1 x → x = x_1