-- Lean 4 proof step from Mathlib.Analysis.InnerProductSpace.OfNorm (goal)
Goal:
𝕜 : Type u_1
inst : RCLike 𝕜
E : Type u_2
inst_1 : NormedAddCommGroup E
inst_2 : NormedSpace 𝕜 E
inst_3 : InnerProductSpaceable E
x y z : E
h1 :
  Eq (α := 𝕜)
    ((𝓚 : (a : ℝ) → 𝕜) (‖x + y + z + (x - z)‖ * ‖x + y + z + (x - z)‖ + ‖x + y + z - (x - z)‖ * ‖x + y + z - (x - z)‖) :
      𝕜)
    ((𝓚 : (a : ℝ) → 𝕜) (2 * (‖x + y + z‖ * ‖x + y + z‖ + ‖x - z‖ * ‖x - z‖)) : 𝕜)
h2 :
  Eq (α := 𝕜)
    ((𝓚 : (a : ℝ) → 𝕜) (‖x + y - z + (x + z)‖ * ‖x + y - z + (x + z)‖ + ‖x + y - z - (x + z)‖ * ‖x + y - z - (x + z)‖) :
      𝕜)
    ((𝓚 : (a : ℝ) → 𝕜) (2 * (‖x + y - z‖ * ‖x + y - z‖ + ‖x + z‖ * ‖x + z‖)) : 𝕜)
h3 :
  Eq (α := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) (‖y + z + z‖ * ‖y + z + z‖ + ‖y + z - z‖ * ‖y + z - z‖) : 𝕜)
    ((𝓚 : (a : ℝ) → 𝕜) (2 * (‖y + z‖ * ‖y + z‖ + ‖z‖ * ‖z‖)) : 𝕜)
h4 :
  Eq (α := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) (‖y - z + z‖ * ‖y - z + z‖ + ‖y - z - z‖ * ‖y - z - z‖) : 𝕜)
    ((𝓚 : (a : ℝ) → 𝕜) (2 * (‖y - z‖ * ‖y - z‖ + ‖z‖ * ‖z‖)) : 𝕜)
h5 :
  Eq (α := 𝕜)
    ((𝓚 : (a : ℝ) → 𝕜)
        (‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) + z + (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z)‖ *
            ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) + z + (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z)‖ +
          ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) + z - (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z)‖ *
            ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) + z - (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z)‖) :
      𝕜)
    ((𝓚 : (a : ℝ) → 𝕜)
        (2 *
          (‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) + z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) + z‖ +
            ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z‖)) :
      𝕜)
h6 :
  Eq (α := 𝕜)
    ((𝓚 : (a : ℝ) → 𝕜)
        (‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) - z + (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z)‖ *
            ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) - z + (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z)‖ +
          ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) - z - (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z)‖ *
            ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) - z - (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z)‖) :
      𝕜)
    ((𝓚 : (a : ℝ) → 𝕜)
        (2 *
          (‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) - z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) - z‖ +
            ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z‖)) :
      𝕜)
h7 :
  Eq (α := 𝕜)
    ((𝓚 : (a : ℝ) → 𝕜)
        (‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z + z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z + z‖ +
          ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z - z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z - z‖) :
      𝕜)
    ((𝓚 : (a : ℝ) → 𝕜)
        (2 *
          (‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ +
            ‖z‖ * ‖z‖)) :
      𝕜)
h8 :
  Eq (α := 𝕜)
    ((𝓚 : (a : ℝ) → 𝕜)
        (‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z + z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z + z‖ +
          ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z - z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z - z‖) :
      𝕜)
    ((𝓚 : (a : ℝ) → 𝕜)
        (2 *
          (‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ * ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ +
            ‖z‖ * ‖z‖)) :
      𝕜)
⊢ 4⁻¹ *
      (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z‖ : 𝕜) -
            HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z‖ : 𝕜) +
          HMul.hMul (β := 𝕜)
            (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜)
              ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) + z‖ : 𝕜))
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) + z‖ : 𝕜) -
        HMul.hMul (β := 𝕜)
          (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜)
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) - z‖ : 𝕜))
          ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I (x + y) - z‖ : 𝕜)) =
    4⁻¹ *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + z‖ : 𝕜) -
              HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x - z‖ : 𝕜) +
            HMul.hMul (β := 𝕜)
              (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜)
                ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z‖ : 𝕜))
              ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z‖ : 𝕜) -
          HMul.hMul (β := 𝕜)
            (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z‖ : 𝕜))
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z‖ : 𝕜)) +
      4⁻¹ *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z‖ : 𝕜) -
              HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z‖ : 𝕜) +
            HMul.hMul (β := 𝕜)
              (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜)
                ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ : 𝕜))
              ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ : 𝕜) -
          HMul.hMul (β := 𝕜)
            (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ : 𝕜))
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ : 𝕜))
have simp : ∀
  (h1 :
    HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z + (x - z)‖ : 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z + (x - z)‖ : 𝕜) +
        HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z - (x - z)‖ : 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z - (x - z)‖ : 𝕜) =
      2 *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z‖ : 𝕜) +
          HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x - z‖ : 𝕜)))
  (h2 :
    HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z + (x + z)‖ : 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z + (x + z)‖ : 𝕜) +
        HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z - (x + z)‖ : 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z - (x + z)‖ : 𝕜) =
      2 *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z‖ : 𝕜) +
          HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + z‖ : 𝕜)))
  (h3 :
    HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z + z‖ : 𝕜) +
        HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z - z‖ : 𝕜) =
      2 *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z‖ : 𝕜) +
          HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖z‖ : 𝕜)))
  (h4 :
    HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z + z‖ : 𝕜) +
        HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z - z‖ : 𝕜) =
      2 *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z‖ : 𝕜) +
          HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖z‖ : 𝕜)))
  (h5 :
    HMul.hMul (α := 𝕜) (β := 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜)
              ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z +
                  (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z)‖ :
            𝕜)
          ((𝓚 : (a : ℝ) → 𝕜)
              ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z +
                  (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z)‖ :
            𝕜) +
        HMul.hMul (α := 𝕜) (β := 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜)
              ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z -
                  (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z)‖ :
            𝕜)
          ((𝓚 : (a : ℝ) → 𝕜)
              ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z -
                  (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z)‖ :
            𝕜) =
      2 *
        (HMul.hMul (α := 𝕜) (β := 𝕜)
            ((𝓚 : (a : ℝ) → 𝕜)
                ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ :
              𝕜)
            ((𝓚 : (a : ℝ) → 𝕜)
                ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ :
              𝕜) +
          HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z‖ : 𝕜)
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z‖ : 𝕜)))
  (h6 :
    HMul.hMul (α := 𝕜) (β := 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜)
              ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z +
                  (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z)‖ :
            𝕜)
          ((𝓚 : (a : ℝ) → 𝕜)
              ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z +
                  (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z)‖ :
            𝕜) +
        HMul.hMul (α := 𝕜) (β := 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜)
              ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z -
                  (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z)‖ :
            𝕜)
          ((𝓚 : (a : ℝ) → 𝕜)
              ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z -
                  (HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z)‖ :
            𝕜) =
      2 *
        (HMul.hMul (α := 𝕜) (β := 𝕜)
            ((𝓚 : (a : ℝ) → 𝕜)
                ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ :
              𝕜)
            ((𝓚 : (a : ℝ) → 𝕜)
                ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ :
              𝕜) +
          HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z‖ : 𝕜)
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z‖ : 𝕜)))
  (h7 :
    HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z + z‖ : 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z + z‖ : 𝕜) +
        HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z - z‖ : 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z - z‖ : 𝕜) =
      2 *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ : 𝕜)
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ : 𝕜) +
          HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖z‖ : 𝕜)))
  (h8 :
    HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z + z‖ : 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z + z‖ : 𝕜) +
        HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z - z‖ : 𝕜)
          ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z - z‖ : 𝕜) =
      2 *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ : 𝕜)
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ : 𝕜) +
          HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖z‖ : 𝕜))),
  4⁻¹ *
      (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y + z‖ : 𝕜) -
            HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + y - z‖ : 𝕜) +
          HMul.hMul (β := 𝕜)
            (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜)
              ((𝓚 : (a : ℝ) → 𝕜)
                  ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ :
                𝕜))
            ((𝓚 : (a : ℝ) → 𝕜)
                ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ :
              𝕜) -
        HMul.hMul (β := 𝕜)
          (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜)
            ((𝓚 : (a : ℝ) → 𝕜)
                ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ :
              𝕜))
          ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ :
            𝕜)) =
    4⁻¹ *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x + z‖ : 𝕜) -
              HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖x - z‖ : 𝕜) +
            HMul.hMul (β := 𝕜)
              (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜)
                ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z‖ : 𝕜))
              ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x + z‖ : 𝕜) -
          HMul.hMul (β := 𝕜)
            (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z‖ : 𝕜))
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I x - z‖ : 𝕜)) +
      4⁻¹ *
        (HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y + z‖ : 𝕜) -
              HMul.hMul (α := 𝕜) (β := 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z‖ : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖y - z‖ : 𝕜) +
            HMul.hMul (β := 𝕜)
              (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜)
                ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ : 𝕜))
              ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y + z‖ : 𝕜) -
          HMul.hMul (β := 𝕜)
            (HMul.hMul (α := 𝕜) (β := 𝕜) (I : 𝕜) ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ : 𝕜))
            ((𝓚 : (a : ℝ) → 𝕜) ‖HSMul.hSMul.{u_1, u_2, u_2} (α := 𝕜) I y - z‖ : 𝕜))
Tactic: simp only [map_add, map_mul, map_ofNat, smul_add] at *
Cleared hypotheses: h1, h2, h3, h4, h5, h6, h7, h8