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]
        

Proof state:
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
| -((2 * ↑π) ^ (2 * k + 1) * I ^ (2 * k + 1))

Next tactic:
congr
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
        

Proof state:
case a
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
| (2 * ↑π) ^ (2 * k + 1) * I ^ (2 * k + 1)

Next tactic:
congr
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
        

Proof state:
case a.a
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
| (2 * ↑π) ^ (2 * k + 1)
case a.a k : ℕ hk : k ≠ 0 x : ℝ hx : x ∈ Icc 0 1 | I ^ (2 * k + 1)

Next tactic:
· skip
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
        · 

Proof state:
case a.a
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
| (2 * ↑π) ^ (2 * k + 1)

Next tactic:
skip
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
        

Proof state:
case a.a
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
| I ^ (2 * k + 1)

Next tactic:
· rw [pow_add, pow_one, pow_mul, 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
        · 

Proof state:
case a.a
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
| I ^ (2 * k + 1)

Next tactic:
rw [pow_add, pow_one, pow_mul, 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]
      

Proof state:
case h.e'_6.e_a.e_a
k : ℕ
hk : k ≠ 0
x : ℝ
hx : x ∈ Icc 0 1
⊢ (-1) ^ k * -1 * I * (2 * ↑π) ^ (2 * k + 1) = -((2 * ↑π) ^ (2 * k + 1) * ((-1) ^ k * 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
  

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))
⊢ HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * Real.sin (2 * π * ↑n * x))
    ((-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 ofReal_two : ((2 : ℝ) : ℂ) = 2 := by norm_cast
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 

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))
⊢ ↑2 = 2

Next tactic:
norm_cast
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
  

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
⊢ HasSum (fun n => 1 / ↑n ^ (2 * k + 1) * Real.sin (2 * π * ↑n * x))
    ((-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:
convert ((hasSum_iff _ _).mp (this.div_const (2 * I))).1
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
  · 

Proof state:
case h.e'_5.h
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
⊢ 1 / ↑x✝ ^ (2 * k + 1) * Real.sin (2 * π * ↑x✝ * x) =
    (1 / ↑x✝ ^ (2 * k + 1) * ((fourier ↑x✝) ↑x - (fourier (-↑x✝)) ↑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
    

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
x✝ : ℕ
⊢ 1 / ↑x✝ ^ (2 * k + 1) * ((fourier ↑x✝) ↑x - (fourier (-↑x✝)) ↑x) / (2 * I) =
    ↑(1 / ↑x✝ ^ (2 * k + 1) * Real.sin (2 * π * ↑x✝ * x))

Next tactic:
rw [ofReal_mul]
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]; 

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
x✝ : ℕ
⊢ 1 / ↑x✝ ^ (2 * k + 1) * ((fourier ↑x✝) ↑x - (fourier (-↑x✝)) ↑x) / (2 * I) =
    ↑(1 / ↑x✝ ^ (2 * k + 1)) * ↑(Real.sin (2 * π * ↑x✝ * x))

Next tactic:
rw [← mul_div]
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]; 

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
x✝ : ℕ
⊢ 1 / ↑x✝ ^ (2 * k + 1) * (((fourier ↑x✝) ↑x - (fourier (-↑x✝)) ↑x) / (2 * I)) =
    ↑(1 / ↑x✝ ^ (2 * k + 1)) * ↑(Real.sin (2 * π * ↑x✝ * x))

Next tactic:
congr
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
    · 

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
⊢ 1 / ↑x✝ ^ (2 * k + 1) = ↑(1 / ↑x✝ ^ (2 * k + 1))

Next tactic:
rw [ofReal_div, ofReal_one, ofReal_pow]
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]; 

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
⊢ 1 / ↑x✝ ^ (2 * k + 1) = 1 / ↑↑x✝ ^ (2 * k + 1)

Next tactic:
rfl
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
    · 

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
⊢ ((fourier ↑x✝) ↑x - (fourier (-↑x✝)) ↑x) / (2 * I) = ↑(Real.sin (2 * π * ↑x✝ * x))

Next tactic:
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]