-- Mathlib/Analysis/CStarAlgebra/Unitization.lean
theorem Unitization.norm_splitMul_snd_sq (x : Unitization 𝕜 E) :
    ‖(Unitization.splitMul 𝕜 E x).snd‖ ^ 2 ≤ ‖(Unitization.splitMul 𝕜 E (star x * x)).snd‖

Proof state:
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ ‖b⋆‖ * ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖ ≤
    1 * ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖

Tactic:
gcongr

Result:
case h
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ ‖b⋆‖ ≤ 1

Proof state:
case intro.intro.calc_1.intro.intro.h₁
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
y : E
hy : y ∈ Metric.closedBall 0 1
⊢ ‖(x⋆ * x).fst‖ * ‖↑1 y‖ ≤ ‖(x⋆ * x).fst‖

Tactic:
simpa only [mul_one] using
  mul_le_mul_of_nonneg_left (mem_closedBall_zero_iff.1 hy) (norm_nonneg (star x * x).fst)

Result:
no goals

Proof state:
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
⊢ ‖(algebraMap 𝕜 (E →L[𝕜] E)) x.fst + (mul 𝕜 E) x.snd‖ ≤
    √‖(algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd‖

Tactic:
rw [← sSup_unitClosedBall_eq_norm]

Result:
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
⊢ sSup ((fun x_1 => ‖((algebraMap 𝕜 (E →L[𝕜] E)) x.fst + (mul 𝕜 E) x.snd) x_1‖) '' Metric.closedBall 0 1) ≤
    √‖(algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd‖

Proof state:
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ ‖b⋆‖ * ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖ ≤
    ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖

Tactic:
nth_rewrite 2 [← one_mul ‖_ + _‖]

Result:
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ ‖b⋆‖ * ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖ ≤
    1 * ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖

Proof state:
case intro.intro.calc_2
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ ‖((algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd) b‖ =
    ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖

Tactic:
simp only [ContinuousLinearMap.add_apply, mul_apply', Unitization.snd_star, Unitization.snd_mul,
  Unitization.fst_mul, Unitization.fst_star, Algebra.algebraMap_eq_smul_one, smul_apply,
  one_apply, smul_add, mul_add, add_mul]

Result:
case intro.intro.calc_2
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ ‖(x.fst⋆ * x.fst) • b + (x.fst⋆ • x.snd * b + x.fst • x.snd⋆ * b + x.snd⋆ * x.snd * b)‖ =
    ‖x.fst⋆ • x.fst • b + x.fst⋆ • (x.snd * b) + (x.snd⋆ * x.fst • b + x.snd⋆ * (x.snd * b))‖

Proof state:
case intro.intro.calc_1.intro.intro.h₂
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
y : E
hy : y ∈ Metric.closedBall 0 1
⊢ ‖↑((mul 𝕜 E) (x⋆ * x).snd) y‖ ≤ ‖(x⋆ * x).snd‖

Tactic:
exact (unit_le_opNorm _ y <| mem_closedBall_zero_iff.1 hy).trans (opNorm_mul_apply_le _ _ _)

Result:
no goals

Proof state:
case intro.intro
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ ‖b⋆‖ * ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖ ≤
    sSup
      ((fun x_1 => ‖((algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd) x_1‖) '' Metric.closedBall 0 1)

Tactic:
calc
  _ ≤ ‖star x.fst • (x.fst • b + x.snd * b) + star x.snd * (x.fst • b + x.snd * b)‖ := by
    nth_rewrite 2 [← one_mul ‖_ + _‖]
    gcongr
    exact (norm_star b).symm ▸ mem_closedBall_zero_iff.1 hb
  _ ≤ sSup (_ '' Metric.closedBall 0 1) := le_csSup ?_ ⟨b, hb, ?_⟩

Result:
case intro.intro.calc_1
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ BddAbove
    ((fun x_1 => ‖((algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd) x_1‖) '' Metric.closedBall 0 1)

case intro.intro.calc_2
𝕜 : Type u_1
E : Type u_2
inst✝⁸ : DenselyNormedField 𝕜
inst✝⁷ : NonUnitalNormedRing E
inst✝⁶ : StarRing E
inst✝⁵ : CStarRing E
inst✝⁴ : NormedSpace 𝕜 E
inst✝³ : IsScalarTower 𝕜 E E
inst✝² : SMulCommClass 𝕜 E E
inst✝¹ : StarRing 𝕜
inst✝ : StarModule 𝕜 E
x : Unitization 𝕜 E
b : E
hb : b ∈ Metric.closedBall 0 1
⊢ ‖((algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd) b‖ =
    ‖x.fst⋆ • (x.fst • b + x.snd * b) + x.snd⋆ * (x.fst • b + x.snd * b)‖