l3lab/ntp-mathlib huggingface dataset:
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      

Proof state:
case h.e'_3.h.e'_1.e_a
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
x✝ : ℕ
⊢ (cexp (2 * ↑π * I * -↑x✝ * ↑x) - cexp (2 * ↑π * I * ↑x✝ * ↑x)) * I / 2 =
    (cexp (-(2 * ↑π * ↑x✝ * ↑x) * I) - cexp (2 * ↑π * ↑x✝ * ↑x * I)) * I / 2

Next tactic:
congr 4
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · 

Proof state:
case h.e'_3.h.e'_1.e_a.e_a.e_a.e_a.e_z
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
x✝ : ℕ
⊢ 2 * ↑π * I * -↑x✝ * ↑x = -(2 * ↑π * ↑x✝ * ↑x) * I

Next tactic:
ring
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · ring
      · 

Proof state:
case h.e'_3.h.e'_1.e_a.e_a.e_a.e_a.e_z
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
x✝ : ℕ
⊢ 2 * ↑π * I * ↑x✝ * ↑x = 2 * ↑π * ↑x✝ * ↑x * I

Next tactic:
ring
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · ring
      · ring
  · 

Proof state:
case h.e'_6
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
⊢ (-1) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / ↑(2 * k + 1)! *
      Polynomial.eval x (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))) =
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x) / (2 * I)).re

Next tactic:
convert (ofReal_re _).symm
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · ring
      · ring
  · convert (ofReal_re _).symm
    

Proof state:
case h.e'_3.h.e'_1
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
⊢ (-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x) / (2 * I) =
    ↑((-1) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / ↑(2 * k + 1)! *
        Polynomial.eval x (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))))

Next tactic:
rw [ofReal_mul, ofReal_div, ofReal_div, ofReal_mul, ofReal_pow, ofReal_pow, ofReal_neg,
      ofReal_nat_cast, ofReal_mul, ofReal_two, ofReal_one, ← div_div, div_I,
      div_mul_eq_mul_div₀]
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · ring
      · ring
  · convert (ofReal_re _).symm
    rw [ofReal_mul, ofReal_div, ofReal_div, ofReal_mul, ofReal_pow, ofReal_pow, ofReal_neg,
      ofReal_nat_cast, ofReal_mul, ofReal_two, ofReal_one, ← div_div, div_I,
      div_mul_eq_mul_div₀]
    

Proof state:
case h.e'_3.h.e'_1
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
⊢ -((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x) * I / 2) =
    (-1) ^ (k + 1) * (2 * ↑π) ^ (2 * k + 1) / 2 / ↑(2 * k + 1)! *
      ↑(Polynomial.eval x (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))))

Next tactic:
have : ∀ α β γ δ : ℂ, α * I * β / γ * δ * I = I ^ 2 * α * β / γ * δ := by intros; ring
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · ring
      · ring
  · convert (ofReal_re _).symm
    rw [ofReal_mul, ofReal_div, ofReal_div, ofReal_mul, ofReal_pow, ofReal_pow, ofReal_neg,
      ofReal_nat_cast, ofReal_mul, ofReal_two, ofReal_one, ← div_div, div_I,
      div_mul_eq_mul_div₀]
    have : ∀ α β γ δ : ℂ, α * I * β / γ * δ * I = I ^ 2 * α * β / γ * δ := by 

Proof state:
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
⊢ ∀ (α β γ δ : ℂ), α * I * β / γ * δ * I = I ^ 2 * α * β / γ * δ

Next tactic:
intros
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · ring
      · ring
  · convert (ofReal_re _).symm
    rw [ofReal_mul, ofReal_div, ofReal_div, ofReal_mul, ofReal_pow, ofReal_pow, ofReal_neg,
      ofReal_nat_cast, ofReal_mul, ofReal_two, ofReal_one, ← div_div, div_I,
      div_mul_eq_mul_div₀]
    have : ∀ α β γ δ : ℂ, α * I * β / γ * δ * I = I ^ 2 * α * β / γ * δ := by intros; 

Proof state:
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
α✝ β✝ γ✝ δ✝ : ℂ
⊢ α✝ * I * β✝ / γ✝ * δ✝ * I = I ^ 2 * α✝ * β✝ / γ✝ * δ✝

Next tactic:
ring
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · ring
      · ring
  · convert (ofReal_re _).symm
    rw [ofReal_mul, ofReal_div, ofReal_div, ofReal_mul, ofReal_pow, ofReal_pow, ofReal_neg,
      ofReal_nat_cast, ofReal_mul, ofReal_two, ofReal_one, ← div_div, div_I,
      div_mul_eq_mul_div₀]
    have : ∀ α β γ δ : ℂ, α * I * β / γ * δ * I = I ^ 2 * α * β / γ * δ := by intros; ring
    

Proof state:
case h.e'_3.h.e'_1
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this✝ :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
this : ∀ (α β γ δ : ℂ), α * I * β / γ * δ * I = I ^ 2 * α * β / γ * δ
⊢ -((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x) * I / 2) =
    (-1) ^ (k + 1) * (2 * ↑π) ^ (2 * k + 1) / 2 / ↑(2 * k + 1)! *
      ↑(Polynomial.eval x (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))))

Next tactic:
rw [this, I_sq]
theorem hasSum_one_div_nat_pow_mul_sin {k : ℕ} (hk : k ≠ 0) {x : ℝ} (hx : x ∈ Icc (0 : ℝ) 1) :
    HasSum (fun n : ℕ => 1 / (n : ℝ) ^ (2 * k + 1) * Real.sin (2 * π * n * x))
      ((-1 : ℝ) ^ (k + 1) * (2 * π) ^ (2 * k + 1) / 2 / (2 * k + 1)! *
        (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))).eval x) := by
  have :
    HasSum (fun n : ℕ => 1 / (n : ℂ) ^ (2 * k + 1) * (fourier n (x : 𝕌) - fourier (-n) (x : 𝕌)))
      ((-1 : ℂ) ^ (k + 1) * I * (2 * π : ℂ) ^ (2 * k + 1) / (2 * k + 1)! *
        bernoulliFun (2 * k + 1) x) := by
    convert
      hasSum_one_div_nat_pow_mul_fourier
        (by linarith [Nat.one_le_iff_ne_zero.mpr hk] : 2 ≤ 2 * k + 1) hx using 1
    · ext1 n
      rw [pow_add (-1 : ℂ), pow_mul (-1 : ℂ), neg_one_sq, one_pow, one_mul, pow_one, ←
        neg_eq_neg_one_mul, ← sub_eq_add_neg]
    · congr
      rw [pow_add, pow_one]
      conv_rhs =>
        rw [mul_pow]
        congr
        congr
        · skip
        · rw [pow_add, pow_one, pow_mul, I_sq]
      ring
  have ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
  convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
  · convert (ofReal_re _).symm
    rw [ofReal_mul]; rw [← mul_div]; congr
    · rw [ofReal_div, ofReal_one, ofReal_pow]; rfl
    · rw [ofReal_sin, ofReal_mul, fourier_coe_apply, fourier_coe_apply, sin, ofReal_one, div_one,
        div_one, ofReal_mul, ofReal_mul, ofReal_two, Int.cast_neg, Int.cast_ofNat,
        ofReal_nat_cast, ← div_div, div_I, div_mul_eq_mul_div₀, ← neg_div, ← neg_mul, neg_sub]
      congr 4
      · ring
      · ring
  · convert (ofReal_re _).symm
    rw [ofReal_mul, ofReal_div, ofReal_div, ofReal_mul, ofReal_pow, ofReal_pow, ofReal_neg,
      ofReal_nat_cast, ofReal_mul, ofReal_two, ofReal_one, ← div_div, div_I,
      div_mul_eq_mul_div₀]
    have : ∀ α β γ δ : ℂ, α * I * β / γ * δ * I = I ^ 2 * α * β / γ * δ := by intros; ring
    rw [this, I_sq]
    

Proof state:
case h.e'_3.h.e'_1
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
this✝ :
  HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * ((fourier ↑n) ↑x - (fourier (-↑n)) ↑x))
    ((-1) ^ (k + 1) * I * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x))
ofReal_two : ↑2 = 2
this : ∀ (α β γ δ : ℂ), α * I * β / γ * δ * I = I ^ 2 * α * β / γ * δ
⊢ -(-1 * (-1) ^ (k + 1) * (2 * ↑π) ^ (2 * k + 1) / ↑(2 * k + 1)! * ↑(bernoulliFun (2 * k + 1) x) / 2) =
    (-1) ^ (k + 1) * (2 * ↑π) ^ (2 * k + 1) / 2 / ↑(2 * k + 1)! *
      ↑(Polynomial.eval x (Polynomial.map (algebraMap ℚ ℝ) (Polynomial.bernoulli (2 * k + 1))))

Next tactic:
rw [bernoulliFun]