{α : Type u_1} →
  {β : α → Type u_2} →
    (r' : Std.DTreeMap.Internal.Impl α β) →
      (motive : Std.DTreeMap.Internal.Impl.Tree α β (r'.size + 1) → Sort u_3) →
        (x : Std.DTreeMap.Internal.Impl.Tree α β (r'.size + 1)) →
          ((r'' : Std.DTreeMap.Internal.Impl α β) →
              (hr''₁ : r''.Balanced) →
                (hr''₂ : r''.size = r'.size + 1) → motive { impl := r'', balanced_impl := hr''₁, size_impl := hr''₂ }) →
            motive x