/-- Given a map `f : G →ₗ[𝕜] MultilinearMap 𝕜 E G'` and an estimate
`H : ∀ x m, ‖f x m‖ ≤ C * ‖x‖ * ∏ i, ‖m i‖`, construct a continuous linear
map from `G` to `ContinuousMultilinearMap 𝕜 E G'`.

In order to lift, e.g., a map `f : (MultilinearMap 𝕜 E G) →ₗ[𝕜] MultilinearMap 𝕜 E' G'`
to a map `(ContinuousMultilinearMap 𝕜 E G) →L[𝕜] ContinuousMultilinearMap 𝕜 E' G'`,
one can apply this construction to `f.comp ContinuousMultilinearMap.toMultilinearMapLinear`
which is a linear map from `ContinuousMultilinearMap 𝕜 E G` to `MultilinearMap 𝕜 E' G'`. -/
def mkContinuousLinear (f : G →ₗ[𝕜] MultilinearMap 𝕜 E G') (C : ℝ)
    (H : ∀ x m, ‖f x m‖ ≤ C * ‖x‖ * ∏ i, ‖m i‖) : G →L[𝕜] ContinuousMultilinearMap 𝕜 E G' :=
  LinearMap.mkContinuous
    { toFun := fun x => (f x).mkContinuous (C * ‖x‖) <| H x
      map_add' := fun x y => by
        ext1
        simp only [_root_.map_add]
        rfl
      map_smul' := fun c x => by
        

Proof state:
𝕜 : Type u
ι : Type v
ι' : Type v'
n : ℕ
E : ι → Type wE
E₁ : ι → Type wE₁
E' : ι' → Type wE'
Ei : Fin (Nat.succ n) → Type wEi
G : Type wG
G' : Type wG'
inst✝¹⁴ : Fintype ι
inst✝¹³ : Fintype ι'
inst✝¹² : NontriviallyNormedField 𝕜
inst✝¹¹ : (i : ι) → NormedAddCommGroup (E i)
inst✝¹⁰ : (i : ι) → NormedSpace 𝕜 (E i)
inst✝⁹ : (i : ι) → NormedAddCommGroup (E₁ i)
inst✝⁸ : (i : ι) → NormedSpace 𝕜 (E₁ i)
inst✝⁷ : (i : ι') → NormedAddCommGroup (E' i)
inst✝⁶ : (i : ι') → NormedSpace 𝕜 (E' i)
inst✝⁵ : (i : Fin (Nat.succ n)) → NormedAddCommGroup (Ei i)
inst✝⁴ : (i : Fin (Nat.succ n)) → NormedSpace 𝕜 (Ei i)
inst✝³ : NormedAddCommGroup G
inst✝² : NormedSpace 𝕜 G
inst✝¹ : NormedAddCommGroup G'
inst✝ : NormedSpace 𝕜 G'
f : G →ₗ[𝕜] MultilinearMap 𝕜 E G'
C : ℝ
H : ∀ (x : G) (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖
c : 𝕜
x : G
⊢ AddHom.toFun
      {
        toFun := fun x =>
          mkContinuous (f x) (C * ‖x‖) (_ : ∀ (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖),
        map_add' :=
          (_ :
            ∀ (x y : G),
              (fun x => mkContinuous (f x) (C * ‖x‖) (_ : ∀ (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖))
                  (x + y) =
                (fun x =>
                      mkContinuous (f x) (C * ‖x‖) (_ : ∀ (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖))
                    x +
                  (fun x =>
                      mkContinuous (f x) (C * ‖x‖) (_ : ∀ (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖))
                    y) }
      (c • x) =
    (RingHom.id 𝕜) c •
      AddHom.toFun
        {
          toFun := fun x =>
            mkContinuous (f x) (C * ‖x‖) (_ : ∀ (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖),
          map_add' :=
            (_ :
              ∀ (x y : G),
                (fun x =>
                      mkContinuous (f x) (C * ‖x‖) (_ : ∀ (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖))
                    (x + y) =
                  (fun x =>
                        mkContinuous (f x) (C * ‖x‖) (_ : ∀ (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖))
                      x +
                    (fun x =>
                        mkContinuous (f x) (C * ‖x‖) (_ : ∀ (m : (i : ι) → E i), ‖(f x) m‖ ≤ C * ‖x‖ * ∏ i : ι, ‖m i‖))
                      y) }
        x

Next tactic:
ext1