-- Mathlib/NumberTheory/Multiplicity.lean
theorem Int.emultiplicity_pow_sub_pow {x y : ℤ} (hxy : ↑p ∣ x - y) (hx : ¬↑p ∣ x) (n : ℕ) :
    emultiplicity (↑p) (x ^ n - y ^ n) = emultiplicity (↑p) (x - y) + emultiplicity p n

Proof state:
case succ.intro.intro.hn
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ¬p ∣ k

Tactic:
rintro ⟨c, rfl⟩

Result:
case succ.intro.intro.hn.intro
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
c : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * (p * c)
⊢ False

Proof state:
case succ
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
⊢ emultiplicity (↑p) (x ^ (n + 1) - y ^ (n + 1)) = emultiplicity (↑p) (x - y) + emultiplicity p (n + 1)

Tactic:
have h : FiniteMultiplicity _ _ := Nat.finiteMultiplicity_iff.mpr ⟨hp.ne_one, n.succ_pos⟩

Result:
case succ
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p n.succ
⊢ emultiplicity (↑p) (x ^ (n + 1) - y ^ (n + 1)) = emultiplicity (↑p) (x - y) + emultiplicity p (n + 1)

Proof state:
case zero
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
⊢ emultiplicity (↑p) (x ^ 0 - y ^ 0) = emultiplicity (↑p) (x - y) + emultiplicity p 0

Tactic:
simp only [emultiplicity_zero, add_top, pow_zero, sub_self]

Result:
no goals

Proof state:
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
⊢ emultiplicity (↑p) (x ^ n - y ^ n) = emultiplicity (↑p) (x - y) + emultiplicity p n

Tactic:
rcases n with - | n

Result:
case zero
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
⊢ emultiplicity (↑p) (x ^ 0 - y ^ 0) = emultiplicity (↑p) (x - y) + emultiplicity p 0

case succ
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
⊢ emultiplicity (↑p) (x ^ (n + 1) - y ^ (n + 1)) = emultiplicity (↑p) (x - y) + emultiplicity p (n + 1)

Proof state:
case succ.intro.intro.hx
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ¬↑p ∣ x ^ p ^ multiplicity p (n + 1)

Tactic:
exact fun h => hx (hp.dvd_of_dvd_pow h)

Result:
no goals

Proof state:
case succ.intro.intro.hxy
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ↑p ∣ x ^ p ^ multiplicity p (n + 1) - y ^ p ^ multiplicity p (n + 1)

Tactic:
rw [← geom_sum₂_mul]

Result:
case succ.intro.intro.hxy
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ↑p ∣ (∑ i ∈ range (p ^ multiplicity p (n + 1)), x ^ i * y ^ (p ^ multiplicity p (n + 1) - 1 - i)) * (x - y)

Proof state:
case succ.intro.intro
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ emultiplicity (↑p) ((x ^ p ^ multiplicity p (n + 1)) ^ k - (y ^ p ^ multiplicity p (n + 1)) ^ k) =
    emultiplicity (↑p) (x - y) + emultiplicity p (n + 1)

Tactic:
rw [emultiplicity_pow_sub_pow_of_prime hp,
  emultiplicity_pow_prime_pow_sub_pow_prime_pow hp hp1 hxy hx, h.emultiplicity_eq_multiplicity]

Result:
case succ.intro.intro.hxy
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ↑p ∣ x ^ p ^ multiplicity p (n + 1) - y ^ p ^ multiplicity p (n + 1)

case succ.intro.intro.hx
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ¬↑p ∣ x ^ p ^ multiplicity p (n + 1)

case succ.intro.intro.hn
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ¬↑p ∣ ↑k

Proof state:
case succ.intro.intro.hn.intro
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
c : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * (p * c)
⊢ False

Tactic:
refine hpn ⟨c, ?_⟩

Result:
case succ.intro.intro.hn.intro
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
c : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * (p * c)
⊢ n + 1 = p ^ (multiplicity p (n + 1) + 1) * c

Proof state:
case succ.intro.intro.hn
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ¬↑p ∣ ↑k

Tactic:
rw [Int.natCast_dvd_natCast]

Result:
case succ.intro.intro.hn
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ ¬p ∣ k

Proof state:
case succ.intro.intro.hn.intro
p : ℕ
hp : Prime ↑p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
c : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * (p * c)
⊢ n + 1 = p ^ (multiplicity p (n + 1) + 1) * c

Tactic:
rwa [pow_succ, mul_assoc]

Result:
no goals

Proof state:
case succ
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
⊢ emultiplicity (↑p) (x ^ (n + 1) - y ^ (n + 1)) = emultiplicity (↑p) (x - y) + emultiplicity p (n + 1)

Tactic:
rcases emultiplicity_eq_coe.mp h.emultiplicity_eq_multiplicity with ⟨⟨k, hk⟩, hpn⟩

Result:
case succ.intro.intro
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ emultiplicity (↑p) (x ^ (n + 1) - y ^ (n + 1)) = emultiplicity (↑p) (x - y) + emultiplicity p (n + 1)

Proof state:
case succ.intro.intro
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ emultiplicity (↑p) (x ^ (n + 1) - y ^ (n + 1)) = emultiplicity (↑p) (x - y) + emultiplicity p (n + 1)

Tactic:
conv_lhs => rw [hk, pow_mul, pow_mul]

Result:
case succ.intro.intro
p : ℕ
hp : Nat.Prime p
hp1 : Odd p
x y : ℤ
hxy : ↑p ∣ x - y
hx : ¬↑p ∣ x
n : ℕ
h : FiniteMultiplicity p (n + 1)
hpn : ¬p ^ (multiplicity p (n + 1) + 1) ∣ n + 1
k : ℕ
hk : n + 1 = p ^ multiplicity p (n + 1) * k
⊢ emultiplicity (↑p) ((x ^ p ^ multiplicity p (n + 1)) ^ k - (y ^ p ^ multiplicity p (n + 1)) ^ k) =
    emultiplicity (↑p) (x - y) + emultiplicity p (n + 1)