Theorem: HurwitzZeta.hurwitzZetaEven_one_sub_two_mul_nat
File: Mathlib/NumberTheory/LSeries/HurwitzZetaValues.lean

Proof steps:
state_before: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
⊢ hurwitzZetaEven (↑x) (1 - 2 * ↑k) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
state_after: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
⊢ hurwitzZetaEven (↑x) (1 - 2 * ↑k) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
tactic: have h1 (n : ℕ) : (2 * k : ℂ) ≠ -n := by
    rw [← Int.cast_ofNat, ← Int.cast_natCast, ← Int.cast_mul, ← Int.cast_natCast n, ← Int.cast_neg,
      Ne, Int.cast_inj, ← Ne]
    refine ne_of_gt ((neg_nonpos_of_nonneg n.cast_nonneg).trans_lt (mul_pos two_pos ?_))
    exact Nat.cast_pos.mpr (Nat.pos_of_ne_zero hk)
state_before: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
⊢ hurwitzZetaEven (↑x) (1 - 2 * ↑k) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
state_after: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
h2 : 2 * ↑k ≠ 1
⊢ hurwitzZetaEven (↑x) (1 - 2 * ↑k) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
tactic: have h2 : (2 * k : ℂ) ≠ 1 := by norm_cast; simp only [mul_eq_one, OfNat.ofNat_ne_one,
    false_and, not_false_eq_true]
state_before: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
h2 : 2 * ↑k ≠ 1
⊢ hurwitzZetaEven (↑x) (1 - 2 * ↑k) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
state_after: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
h2 : 2 * ↑k ≠ 1
h3 : (2 * ↑k).Gammaℂ ≠ 0
⊢ hurwitzZetaEven (↑x) (1 - 2 * ↑k) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
tactic: have h3 : Gammaℂ (2 * k) ≠ 0 := by
    refine mul_ne_zero (mul_ne_zero two_ne_zero ?_) (Gamma_ne_zero h1)
    simp only [ne_eq, cpow_eq_zero_iff, mul_eq_zero, OfNat.ofNat_ne_zero, ofReal_eq_zero,
      pi_ne_zero, Nat.cast_eq_zero, false_or, false_and, not_false_eq_true]
state_before: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
h2 : 2 * ↑k ≠ 1
h3 : (2 * ↑k).Gammaℂ ≠ 0
⊢ hurwitzZetaEven (↑x) (1 - 2 * ↑k) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
state_after: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
h2 : 2 * ↑k ≠ 1
h3 : (2 * ↑k).Gammaℂ ≠ 0
⊢ Complex.cos (↑π * (2 * ↑k) / 2) * (-1) ^ (k + 1) / (2 * ↑k) *
      Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k))) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
tactic: rw [hurwitzZetaEven_one_sub _ h1 (Or.inr h2), ← Gammaℂ, cosZeta_two_mul_nat' hk hx, ← mul_assoc,
    ← mul_div_assoc, mul_assoc, mul_div_cancel_left₀ _ h3, ← mul_div_assoc]
state_before: k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
h2 : 2 * ↑k ≠ 1
h3 : (2 * ↑k).Gammaℂ ≠ 0
⊢ Complex.cos (↑π * (2 * ↑k) / 2) * (-1) ^ (k + 1) / (2 * ↑k) *
      Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k))) =
    -1 / (2 * ↑k) * Polynomial.eval (↑x) (Polynomial.map (algebraMap ℚ ℂ) (Polynomial.bernoulli (2 * k)))
state_after: case e_a.e_a
k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
h2 : 2 * ↑k ≠ 1
h3 : (2 * ↑k).Gammaℂ ≠ 0
⊢ Complex.cos (↑π * (2 * ↑k) / 2) * (-1) ^ (k + 1) = -1
tactic: congr 2
state_before: case e_a.e_a
k : ℕ
x : ℝ
hk : k ≠ 0
hx : x ∈ Icc 0 1
h1 : ∀ (n : ℕ), 2 * ↑k ≠ -↑n
h2 : 2 * ↑k ≠ 1
h3 : (2 * ↑k).Gammaℂ ≠ 0
⊢ Complex.cos (↑π * (2 * ↑k) / 2) * (-1) ^ (k + 1) = -1
state_after: no goals
tactic: rw [mul_div_assoc, mul_div_cancel_left₀ _ two_ne_zero, ← ofReal_natCast, ← ofReal_mul,
    ← ofReal_cos, mul_comm π, ← sub_zero (k * π), cos_nat_mul_pi_sub, Real.cos_zero, mul_one,
    ofReal_pow, ofReal_neg, ofReal_one, pow_succ, mul_neg_one, mul_neg, ← mul_pow, neg_one_mul,
    neg_neg, one_pow]