{motive : Lean.Meta.RefinedDiscrTree.Key → Sort u} →
  (t : Lean.Meta.RefinedDiscrTree.Key) →
    t.ctorIdx = 10 →
      ((typeName : Lean.Name) → (idx nargs : ℕ) → motive (Lean.Meta.RefinedDiscrTree.Key.proj typeName idx nargs)) →
        motive t