{motive : Lean.Grind.CommRing.Poly → Sort u} →
  (t : Lean.Grind.CommRing.Poly) →
    ((t : Lean.Grind.CommRing.Poly) → Lean.Grind.CommRing.Poly.below t → motive t) →
      motive t ×' Lean.Grind.CommRing.Poly.below t