theorem sub_one_pow_totient_lt_cyclotomic_eval {n : ℕ} {q : ℝ} (hn' : 2 ≤ n) (hq' : 1 < q) :
    (q - 1) ^ totient n < (cyclotomic n ℝ).eval q := by
  have hn : 0 < n := pos_of_gt hn'
  have hq := zero_lt_one.trans hq'
  have hfor : ∀ ζ' ∈ primitiveRoots n ℂ, q - 1 ≤ ‖↑q - ζ'‖ := by
    intro ζ' hζ'
    rw [mem_primitiveRoots hn] at hζ'
    convert norm_sub_norm_le (↑q) ζ'
    · rw [Complex.norm_real, Real.norm_of_nonneg hq.le]
    · rw [hζ'.norm'_eq_one hn.ne']
  let ζ := Complex.exp (2 * ↑Real.pi * Complex.I / ↑n)
  have hζ : IsPrimitiveRoot ζ n := Complex.isPrimitiveRoot_exp n hn.ne'
  have hex : ∃ ζ' ∈ primitiveRoots n ℂ, q - 1 < ‖↑q - ζ'‖ := by
    refine' ⟨ζ, (mem_primitiveRoots hn).mpr hζ, _⟩
    suffices ¬SameRay ℝ (q : ℂ) ζ by
      convert lt_norm_sub_of_not_sameRay this <;>
        simp only [hζ.norm'_eq_one hn.ne', Real.norm_of_nonneg hq.le, Complex.norm_real]
    rw [Complex.sameRay_iff]
    push_neg
    refine' ⟨mod_cast hq.ne', hζ.ne_zero hn.ne', _⟩
    rw [Complex.arg_ofReal_of_nonneg hq.le, Ne.def, eq_comm, hζ.arg_eq_zero_iff hn.ne']
    clear_value ζ
    rintro rfl
    linarith [hζ.unique IsPrimitiveRoot.one]
  have : ¬eval (↑q) (cyclotomic n ℂ) = 0 := by
    erw [cyclotomic.eval_apply q n (algebraMap ℝ ℂ)]
    simpa only [Complex.coe_algebraMap, Complex.ofReal_eq_zero] using (cyclotomic_pos' n hq').ne'
  suffices Units.mk0 (Real.toNNReal (q - 1)) (by simp [hq']) ^ totient n <
      Units.mk0 ‖(cyclotomic n ℂ).eval ↑q‖₊ (by simp [this]) by
    simp only [← Units.val_lt_val, Units.val_pow_eq_pow_val, Units.val_mk0, ← NNReal.coe_lt_coe,
      hq'.le, Real.toNNReal_lt_toNNReal_iff_of_nonneg, coe_nnnorm, Complex.norm_eq_abs,
      NNReal.coe_pow, Real.coe_toNNReal', max_eq_left, sub_nonneg] at this
    convert this
    erw [cyclotomic.eval_apply q n (algebraMap ℝ ℂ), eq_comm]
    simp only [cyclotomic_nonneg n hq'.le, Complex.coe_algebraMap, Complex.abs_ofReal, abs_eq_self]
  simp only [cyclotomic_eq_prod_X_sub_primitiveRoots hζ, eval_prod, eval_C, eval_X, eval_sub,
    nnnorm_prod, Units.mk0_prod]
  convert Finset.prod_lt_prod' (M := NNRealˣ) _ _
  swap; · exact fun _ => Units.mk0 (Real.toNNReal (q - 1)) (by simp [hq'])
  · simp only [Complex.card_primitiveRoots, prod_const, card_attach]
  · simp only [Subtype.coe_mk, Finset.mem_attach, forall_true_left, Subtype.forall, ←
      Units.val_le_val, ← NNReal.coe_le_coe, Complex.abs.nonneg, hq'.le, Units.val_mk0,
      Real.coe_toNNReal', coe_nnnorm, Complex.norm_eq_abs, max_le_iff, tsub_le_iff_right]
    intro x hx
    simpa only [and_true_iff, tsub_le_iff_right] using hfor x hx
  · simp only [Subtype.coe_mk, Finset.mem_attach, exists_true_left, Subtype.exists, ←
      NNReal.coe_lt_coe, ← Units.val_lt_val, Units.val_mk0 _, coe_nnnorm]
    

Proof state:
case convert_6
n : ℕ
q : ℝ
hn' : 2 ≤ n
hq' : 1 < q
hn : 0 < n
hq : 0 < q
hfor : ∀ ζ' ∈ primitiveRoots n ℂ, q - 1 ≤ ‖↑q - ζ'‖
ζ : ℂ := Complex.exp (2 * ↑Real.pi * Complex.I / ↑n)
hζ : IsPrimitiveRoot ζ n
hex : ∃ ζ' ∈ primitiveRoots n ℂ, q - 1 < ‖↑q - ζ'‖
this : ¬eval (↑q) (cyclotomic n ℂ) = 0
⊢ ∃ a, ∃ (_ : a ∈ primitiveRoots n ℂ), True ∧ ↑(Real.toNNReal (q - 1)) < ‖↑q - a‖

Next tactic:
simpa [hq'.le, Real.coe_toNNReal', max_eq_left, sub_nonneg] using hex