-- 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:
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
⊢ ‖(x⋆ * x).fst‖ + ‖(x⋆ * x).snd‖ ∈
    upperBounds
      ((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:
rintro _ ⟨y, hy, rfl⟩

Result:
case intro.intro.calc_1.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
y : E
hy : y ∈ Metric.closedBall 0 1
⊢ (fun x_1 => ‖((algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd) x_1‖) y ≤
    ‖(x⋆ * x).fst‖ + ‖(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
⊢ 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‖

Tactic:
refine csSup_le ((Metric.nonempty_closedBall.2 zero_le_one).image _) ?_

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 ∈ (fun x_1 => ‖((algebraMap 𝕜 (E →L[𝕜] E)) x.fst + (mul 𝕜 E) x.snd) x_1‖) '' Metric.closedBall 0 1,
    b ≤ √‖(algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd‖

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
⊢ ‖↑((algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst) y‖ ≤ ‖(x⋆ * x).fst‖

Tactic:
rw [Algebra.algebraMap_eq_smul_one]

Result:
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‖

Proof state:
case intro.intro.calc_1.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
y : E
hy : y ∈ Metric.closedBall 0 1
⊢ ‖↑((algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst) y‖ + ‖↑((mul 𝕜 E) (x⋆ * x).snd) y‖ ≤ ‖(x⋆ * x).fst‖ + ‖(x⋆ * x).snd‖

Tactic:
gcongr

Result:
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
⊢ ‖↑((algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst) y‖ ≤ ‖(x⋆ * x).fst‖

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‖

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
⊢ ‖((algebraMap 𝕜 (E →L[𝕜] E)) x.fst + (mul 𝕜 E) x.snd) b‖ ≤
    √‖(algebraMap 𝕜 (E →L[𝕜] E)) (x⋆ * x).fst + (mul 𝕜 E) (x⋆ * x).snd‖

Tactic:
rw [← Real.sqrt_sq (norm_nonneg _), Real.sqrt_le_sqrt_iff (norm_nonneg _), sq,
  ← CStarRing.norm_star_mul_self, ContinuousLinearMap.add_apply, star_add, mul_apply',
  Algebra.algebraMap_eq_smul_one, ContinuousLinearMap.smul_apply,
  ContinuousLinearMap.one_apply, star_mul, star_smul, add_mul, smul_mul_assoc, ← mul_smul_comm,
  mul_assoc, ← mul_add, ← sSup_unitClosedBall_eq_norm]

Result:
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)

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:
refine (norm_mul_le _ _).trans ?_

Result:
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)