Theorem: _private.Mathlib.NumberTheory.FLT.Three.0.fermatLastTheoremThree_of_dvd_a_of_gcd_eq_one_of_case2
File: Mathlib/NumberTheory/FLT/Three.lean

Proof steps:
state_before: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
⊢ a ^ 3 + b ^ 3 + c ^ 3 ≠ 0
state_after: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
⊢ False
tactic: intro HF
state_before: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
⊢ False
state_after: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
⊢ 3 ∣ 1
tactic: apply (show ¬(3 ∣ (1 : ℤ)) by decide)
state_before: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
⊢ 3 ∣ 1
state_after: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
⊢ 3 ∣ {a, b, c}.gcd id
tactic: rw [← Hgcd]
state_before: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
⊢ 3 ∣ {a, b, c}.gcd id
state_after: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
hx : x ∈ {a, b, c}
⊢ 3 ∣ id x
tactic: refine dvd_gcd (fun x hx ↦ ?_)
state_before: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
hx : x ∈ {a, b, c}
⊢ 3 ∣ id x
state_after: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
hx : x = a ∨ x = b ∨ x = c
⊢ 3 ∣ id x
tactic: simp only [mem_insert, mem_singleton] at hx
state_before: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
hx : x = a ∨ x = b ∨ x = c
⊢ 3 ∣ id x
state_after: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
hx : x = a ∨ x = b ∨ x = c
h3b : 3 ∣ b
⊢ 3 ∣ id x
tactic: have h3b : 3 ∣ b := by
    refine three_dvd_b_of_dvd_a_of_gcd_eq_one_of_case2 ha ?_ h3a HF H
    simp only [← Hgcd, gcd_insert, gcd_singleton, id_eq, ← Int.abs_eq_normalize, abs_neg]
state_before: a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
hx : x = a ∨ x = b ∨ x = c
h3b : 3 ∣ b
⊢ 3 ∣ id x
state_after: case inl
a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
h3b : 3 ∣ b
hx : x = a
⊢ 3 ∣ id x

case inr.inl
a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
h3b : 3 ∣ b
hx : x = b
⊢ 3 ∣ id x

case inr.inr
a b c : ℤ
ha : a ≠ 0
h3a : 3 ∣ a
Hgcd : {a, b, c}.gcd id = 1
H : ∀ (a b c : ℤ), c ≠ 0 → ¬3 ∣ a → ¬3 ∣ b → 3 ∣ c → IsCoprime a b → a ^ 3 + b ^ 3 ≠ c ^ 3
HF : a ^ 3 + b ^ 3 + c ^ 3 = 0
x : ℤ
h3b : 3 ∣ b
hx : x = c
⊢ 3 ∣ id x
tactic: rcases hx with hx | hx | hx