∀ {α β : Type u_1} [inst : Std.Iterator α Id β] (it : Std.Iter β) (n : (fun x => ℕ) it) (it' : Std.Iter β),
  it.IsPlausibleStep (Std.IterStep.skip it') →
    InvImage (Prod.Lex WellFoundedRelation.rel Std.IterM.TerminationMeasures.Productive.Rel)
      (fun p => (p.snd, p.fst.finitelyManySkips!)) ⟨it', n⟩ ⟨it, n⟩