∀ {α : Type u_1} {β : α → Type u_2} (r' : Std.DTreeMap.Internal.Impl α β) (szr : ℕ) (k'' : α) (v'' : β k'')
  (l'' r'' : Std.DTreeMap.Internal.Impl α β)
  (motive :
    Std.DTreeMap.Internal.Impl.Tree α β (r'.size + 1 + (Std.DTreeMap.Internal.Impl.inner szr k'' v'' l'' r'').size) →
      Sort u_3)
  (ℓ : Std.DTreeMap.Internal.Impl α β) (hℓ₁ : ℓ.Balanced)
  (hℓ₂ : ℓ.size = r'.size + 1 + (Std.DTreeMap.Internal.Impl.inner szr k'' v'' l'' r'').size)
  (h_1 :
    (ℓ : Std.DTreeMap.Internal.Impl α β) →
      (hℓ₁ : ℓ.Balanced) →
        (hℓ₂ : ℓ.size = r'.size + 1 + (Std.DTreeMap.Internal.Impl.inner szr k'' v'' l'' r'').size) →
          motive { impl := ℓ, balanced_impl := hℓ₁, size_impl := hℓ₂ }),
  (match { impl := ℓ, balanced_impl := hℓ₁, size_impl := hℓ₂ } with
    | { impl := ℓ, balanced_impl := hℓ₁, size_impl := hℓ₂ } => h_1 ℓ hℓ₁ hℓ₂) =
    h_1 ℓ hℓ₁ hℓ₂