-- Mathlib/Data/Real/Pi/Irrational.lean
theorem irrational_pi : Irrational π

Proof state:
case intro.intro.intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
j : ∀ᶠ (n : ℕ) in atTop, ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
hn' : 0 < ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2)
z : ℤ
hz : eval₂ (Int.castRingHom ℝ) (↑a / ↑b) (sinPoly n) * ↑b ^ (2 * n + 1) = ↑z
e :
  I n (π / 2) * (π / 2) ^ (2 * n + 1) =
    ↑n ! *
      (eval₂ (Int.castRingHom ℝ) (π / 2) (sinPoly n) * sin (π / 2) +
        eval₂ (Int.castRingHom ℝ) (π / 2) (cosPoly n) * cos (π / 2))
⊢ False

Tactic:
rw [cos_pi_div_two, sin_pi_div_two, mul_zero, mul_one, add_zero] at e

Result:
case intro.intro.intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
j : ∀ᶠ (n : ℕ) in atTop, ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
hn' : 0 < ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2)
z : ℤ
hz : eval₂ (Int.castRingHom ℝ) (↑a / ↑b) (sinPoly n) * ↑b ^ (2 * n + 1) = ↑z
e : I n (π / 2) * (π / 2) ^ (2 * n + 1) = ↑n ! * eval₂ (Int.castRingHom ℝ) (π / 2) (sinPoly n)
⊢ False

Proof state:
case h
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
this : ∀ᶠ (a_1 : ℕ) in atTop, ↑a ^ (2 * a_1 + 1) / ↑a_1 ! < 1 / 2
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! < 1 / 2
⊢ ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1

Tactic:
rw [lt_div_iff₀ (zero_lt_two : (0 : ℝ) < 2)] at hn

Result:
case h
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
this : ∀ᶠ (a_1 : ℕ) in atTop, ↑a ^ (2 * a_1 + 1) / ↑a_1 ! < 1 / 2
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * 2 < 1
⊢ ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1

Proof state:
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
j : ∀ᶠ (n : ℕ) in atTop, ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
hn' : 0 < ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2)
z : ℤ
hz : eval₂ (Int.castRingHom ℝ) (↑a / ↑b) (sinPoly n) * ↑b ^ (2 * n + 1) = ↑z
e : I n (π / 2) * ↑a ^ (2 * n + 1) = ↑n ! * eval₂ (Int.castRingHom ℝ) (π / 2) (sinPoly n) * ↑b ^ (2 * n + 1)
⊢ ↑a ^ (2 * n + 1) * I n (π / 2) = eval₂ (Int.castRingHom ℝ) (π / 2) (sinPoly n) * ↑b ^ (2 * n + 1) * ↑n !

Tactic:
linear_combination e

Result:
no goals

Proof state:
case intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
⊢ False

Tactic:
have k (n : ℕ) : 0 < (a : ℝ) ^ (2 * n + 1) / n ! := by positivity

Result:
case intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
⊢ False

Proof state:
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
⊢ 0 < ↑a

Tactic:
have : 0 < (a : ℝ) / b := h ▸ pi_div_two_pos

Result:
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
this : 0 < ↑a / ↑b
⊢ 0 < ↑a

Proof state:
case intro.intro.intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
j : ∀ᶠ (n : ℕ) in atTop, ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
hn' : 0 < ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2)
z : ℤ
hz : eval₂ (Int.castRingHom ℝ) (↑a / ↑b) (sinPoly n) * ↑b ^ (2 * n + 1) = ↑z
e : I n (π / 2) * (π / 2) ^ (2 * n + 1) = ↑n ! * eval₂ (Int.castRingHom ℝ) (π / 2) (sinPoly n)
this✝ : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) = eval₂ (Int.castRingHom ℝ) (π / 2) (sinPoly n) * ↑b ^ (2 * n + 1)
this : 0 < z ∧ z < 1
⊢ False

Tactic:
omega

Result:
no goals

Proof state:
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
n : ℕ
⊢ 0 < ↑a ^ (2 * n + 1) / ↑n !

Tactic:
positivity

Result:
no goals

Proof state:
case intro.intro.intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
j : ∀ᶠ (n : ℕ) in atTop, ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
hn' : 0 < ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2)
z : ℤ
hz : eval₂ (Int.castRingHom ℝ) (↑a / ↑b) (sinPoly n) * ↑b ^ (2 * n + 1) = ↑z
⊢ False

Tactic:
have e := sinPoly_add_cosPoly_eval (π / 2) n

Result:
case intro.intro.intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
j : ∀ᶠ (n : ℕ) in atTop, ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
hn' : 0 < ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2)
z : ℤ
hz : eval₂ (Int.castRingHom ℝ) (↑a / ↑b) (sinPoly n) * ↑b ^ (2 * n + 1) = ↑z
e :
  I n (π / 2) * (π / 2) ^ (2 * n + 1) =
    ↑n ! *
      (eval₂ (Int.castRingHom ℝ) (π / 2) (sinPoly n) * sin (π / 2) +
        eval₂ (Int.castRingHom ℝ) (π / 2) (cosPoly n) * cos (π / 2))
⊢ False

Proof state:
h' : ¬Irrational (π / 2)
⊢ False

Tactic:
obtain ⟨a, b, hb, h⟩ := not_irrational_exists_rep h'

Result:
case intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
⊢ False

Proof state:
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
this : 0 < ↑a / ↑b
⊢ 0 < ↑a

Tactic:
rwa [lt_div_iff₀ (by positivity), zero_mul] at this

Result:
no goals

Proof state:
case intro.intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
j : ∀ᶠ (n : ℕ) in atTop, ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
hn' : 0 < ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2)
⊢ False

Tactic:
obtain ⟨z, hz⟩ : ∃ z : ℤ, (sinPoly n).eval₂ (Int.castRingHom ℝ) (a / b) * b ^ (2 * n + 1) = z :=
  is_integer a b ((sinPoly_natDegree_le _).trans (by omega))

Result:
case intro.intro.intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
k : ∀ (n : ℕ), 0 < ↑a ^ (2 * n + 1) / ↑n !
j : ∀ᶠ (n : ℕ) in atTop, ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
n : ℕ
hn : ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2) < 1
hn' : 0 < ↑a ^ (2 * n + 1) / ↑n ! * I n (π / 2)
z : ℤ
hz : eval₂ (Int.castRingHom ℝ) (↑a / ↑b) (sinPoly n) * ↑b ^ (2 * n + 1) = ↑z
⊢ False

Proof state:
case intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
⊢ False

Tactic:
have ha : (0 : ℝ) < a := by
  have : 0 < (a : ℝ) / b := h ▸ pi_div_two_pos
  rwa [lt_div_iff₀ (by positivity), zero_mul] at this

Result:
case intro.intro.intro
h' : ¬Irrational (π / 2)
a : ℤ
b : ℕ
hb : 0 < b
h : π / 2 = ↑a / ↑b
ha : 0 < ↑a
⊢ False