theorem extracted_formal_statement_173.{u_3, u_2, u_1} {E₁ : Type u_1} {E₂ : Type u_2} {F : Type u_3}
  [inst : NormedAddCommGroup E₁] [inst_1 : InnerProductSpace ℝ E₁] [inst_2 : FiniteDimensional ℝ E₁]
  [inst_3 : NormedAddCommGroup E₂] [inst_4 : InnerProductSpace ℝ E₂] [inst_5 : FiniteDimensional ℝ E₂]
  [inst_6 : NormedAddCommGroup F] [inst_7 : InnerProductSpace ℝ F] [inst_8 : FiniteDimensional ℝ F]
  {admm : ADMM E₁ E₂ F} {admm_kkt : Existance_of_kkt admm} [inst_9 : Setting E₁ E₂ F admm admm_kkt] (n : ℕ) :
  let A_e_sum := (OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1));
  let A_x_sum := -(OptProblem.A₂ E₁) (ADMM.x₂ E₁ F n - ADMM.x₂ E₁ F (n + 1));
  let ey' := ey (n + 1);
  let Ae1 := (OptProblem.A₁ E₂) (e₁ (n + 1));
  ⟪ey (n + 1), -((OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1)))⟫_ℝ -
          (1 - ADMM.τ E₁ E₂ F) * ADMM.ρ E₁ E₂ F *
            ‖(OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1))‖ ^ 2 +
        ADMM.ρ E₁ E₂ F *
          ⟪-(OptProblem.A₂ E₁) (ADMM.x₂ E₁ F n - ADMM.x₂ E₁ F (n + 1)), (OptProblem.A₁ E₂) (e₁ (n + 1))⟫_ℝ =
      ⟪ey', -A_e_sum⟫_ℝ - (1 - ADMM.τ E₁ E₂ F) * ADMM.ρ E₁ E₂ F * ⟪A_e_sum, A_e_sum⟫_ℝ +
        ADMM.ρ E₁ E₂ F * ⟪A_x_sum, Ae1⟫_ℝ →
    ⟪ey (n + 1), -((OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1)))⟫_ℝ -
          (1 - ADMM.τ E₁ E₂ F) * ADMM.ρ E₁ E₂ F * RCLike.re ⟪A_e_sum, A_e_sum⟫_ℝ +
        ADMM.ρ E₁ E₂ F *
          ⟪-(OptProblem.A₂ E₁) (ADMM.x₂ E₁ F n - ADMM.x₂ E₁ F (n + 1)), (OptProblem.A₁ E₂) (e₁ (n + 1))⟫_ℝ =
      ⟪ey', -A_e_sum⟫_ℝ - (1 - ADMM.τ E₁ E₂ F) * ADMM.ρ E₁ E₂ F * ⟪A_e_sum, A_e_sum⟫_ℝ +
        ADMM.ρ E₁ E₂ F * ⟪A_x_sum, Ae1⟫_ℝ := sorry

State before:
E₁ : Type u_1
E₂ : Type u_2
F : Type u_3
inst✝⁹ : NormedAddCommGroup E₁
inst✝⁸ : InnerProductSpace ℝ E₁
inst✝⁷ : FiniteDimensional ℝ E₁
inst✝⁶ : NormedAddCommGroup E₂
inst✝⁵ : InnerProductSpace ℝ E₂
inst✝⁴ : FiniteDimensional ℝ E₂
inst✝³ : NormedAddCommGroup F
inst✝² : InnerProductSpace ℝ F
inst✝¹ : FiniteDimensional ℝ F
admm : ADMM E₁ E₂ F
admm_kkt : Existance_of_kkt admm
inst✝ : Setting E₁ E₂ F admm admm_kkt
n : ℕ
A_e_sum : F := (OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1))
A_x_sum : F := -(OptProblem.A₂ E₁) (ADMM.x₂ E₁ F n - ADMM.x₂ E₁ F (n + 1))
ey' : F := ey (n + 1)
Ae1 : F := (OptProblem.A₁ E₂) (e₁ (n + 1))
Ae2 : F := (OptProblem.A₂ E₁) (e₂ (n + 1))
⊢ ⟪ey (n + 1), -((OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1)))⟫_ℝ -
        (1 - ADMM.τ E₁ E₂ F) * ADMM.ρ E₁ E₂ F *
          ‖(OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1))‖ ^ 2 +
      ADMM.ρ E₁ E₂ F *
        ⟪-(OptProblem.A₂ E₁) (ADMM.x₂ E₁ F n - ADMM.x₂ E₁ F (n + 1)), (OptProblem.A₁ E₂) (e₁ (n + 1))⟫_ℝ =
    ⟪ey', -A_e_sum⟫_ℝ - (1 - ADMM.τ E₁ E₂ F) * ADMM.ρ E₁ E₂ F * ⟪A_e_sum, A_e_sum⟫_ℝ + ADMM.ρ E₁ E₂ F * ⟪A_x_sum, Ae1⟫_ℝ

Tactic: rw [norm_sq_eq_inner (𝕜 := ℝ) (A_e_sum)]

State after:
[E₁ : Type u_1
 E₂ : Type u_2
 F : Type u_3
 inst✝⁹ : NormedAddCommGroup E₁
 inst✝⁸ : InnerProductSpace ℝ E₁
 inst✝⁷ : FiniteDimensional ℝ E₁
 inst✝⁶ : NormedAddCommGroup E₂
 inst✝⁵ : InnerProductSpace ℝ E₂
 inst✝⁴ : FiniteDimensional ℝ E₂
 inst✝³ : NormedAddCommGroup F
 inst✝² : InnerProductSpace ℝ F
 inst✝¹ : FiniteDimensional ℝ F
 admm : ADMM E₁ E₂ F
 admm_kkt : Existance_of_kkt admm
 inst✝ : Setting E₁ E₂ F admm admm_kkt
 n : ℕ
 A_e_sum : F := (OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1))
 A_x_sum : F := -(OptProblem.A₂ E₁) (ADMM.x₂ E₁ F n - ADMM.x₂ E₁ F (n + 1))
 ey' : F := ey (n + 1)
 Ae1 : F := (OptProblem.A₁ E₂) (e₁ (n + 1))
 Ae2 : F := (OptProblem.A₂ E₁) (e₂ (n + 1))
 ⊢ ⟪ey (n + 1), -((OptProblem.A₁ E₂) (e₁ (n + 1)) + (OptProblem.A₂ E₁) (e₂ (n + 1)))⟫_ℝ -
         (1 - ADMM.τ E₁ E₂ F) * ADMM.ρ E₁ E₂ F * RCLike.re ⟪A_e_sum, A_e_sum⟫_ℝ +
       ADMM.ρ E₁ E₂ F *
         ⟪-(OptProblem.A₂ E₁) (ADMM.x₂ E₁ F n - ADMM.x₂ E₁ F (n + 1)), (OptProblem.A₁ E₂) (e₁ (n + 1))⟫_ℝ =
     ⟪ey', -A_e_sum⟫_ℝ - (1 - ADMM.τ E₁ E₂ F) * ADMM.ρ E₁ E₂ F * ⟪A_e_sum, A_e_sum⟫_ℝ +
       ADMM.ρ E₁ E₂ F * ⟪A_x_sum, Ae1⟫_ℝ]

Relevant lemmas:
InnerProductSpace.norm_sq_eq_inner : ∀ {𝕜 : Type u_4} {E : Type u_5} {inst : RCLike 𝕜}
  {inst_10 : SeminormedAddCommGroup E} [self : InnerProductSpace 𝕜 E] (x : E), ‖x‖ ^ 2 = RCLike.re ⟪x, x⟫_𝕜