-- Mathlib/RingTheory/UniqueFactorizationDomain/FactorSet.lean
theorem count_factors_eq_find_of_dvd_pow {a p : Associates α}
    (hp : Irreducible p) [∀ n : ℕ, Decidable (a ∣ p ^ n)] {n : ℕ} (h : a ∣ p ^ n) :
    @Nat.find (fun n => a ∣ p ^ n) _ ⟨n, h⟩ = p.count a.factors

Proof state:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ Nat.find ⋯ ≤ p.count a.factors

Tactic:
refine Nat.find_le ⟨1, ?_⟩

Result:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ p ^ p.count a.factors = a * 1

Proof state:
case a.inr
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
hph : p ^ Nat.find ⋯ ≠ 0
hα : Nontrivial α
⊢ p.count a.factors ≤ Nat.find ⋯

Tactic:
convert count_le_count_of_le hph hp (@Nat.find_spec (fun n => a ∣ p ^ n) _ ⟨n, h⟩)

Result:
case h.e'_4
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
hph : p ^ Nat.find ⋯ ≠ 0
hα : Nontrivial α
⊢ Nat.find ⋯ = p.count (p ^ Nat.find ⋯).factors

Proof state:
case a.inl
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
hph : p ^ Nat.find ⋯ ≠ 0
hα : Subsingleton α
⊢ p.count a.factors ≤ Nat.find ⋯

Tactic:
simp [eq_iff_true_of_subsingleton] at hph

Result:
no goals

Proof state:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ a = p ^ p.count a.factors

Tactic:
exact eq_pow_count_factors_of_dvd_pow hp h

Result:
no goals

Proof state:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
hph : p ^ Nat.find ⋯ ≠ 0
⊢ p.count a.factors ≤ Nat.find ⋯

Tactic:
rcases subsingleton_or_nontrivial α with hα | hα

Result:
case a.inl
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
hph : p ^ Nat.find ⋯ ≠ 0
hα : Subsingleton α
⊢ p.count a.factors ≤ Nat.find ⋯

case a.inr
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
hph : p ^ Nat.find ⋯ ≠ 0
hα : Nontrivial α
⊢ p.count a.factors ≤ Nat.find ⋯

Proof state:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ p ^ p.count a.factors = a

Tactic:
symm

Result:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ a = p ^ p.count a.factors

Proof state:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ p.count a.factors ≤ Nat.find ⋯

Tactic:
have hph := pow_ne_zero (@Nat.find (fun n => a ∣ p ^ n) _ ⟨n, h⟩) hp.ne_zero

Result:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
hph : p ^ Nat.find ⋯ ≠ 0
⊢ p.count a.factors ≤ Nat.find ⋯

Proof state:
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ Nat.find ⋯ = p.count a.factors

Tactic:
apply le_antisymm

Result:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ Nat.find ⋯ ≤ p.count a.factors

case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ p.count a.factors ≤ Nat.find ⋯

Proof state:
case h.e'_4
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
hph : p ^ Nat.find ⋯ ≠ 0
hα : Nontrivial α
⊢ Nat.find ⋯ = p.count (p ^ Nat.find ⋯).factors

Tactic:
rw [count_pow hp.ne_zero hp, count_self hp, mul_one]

Result:
no goals

Proof state:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ p ^ p.count a.factors = a * 1

Tactic:
rw [mul_one]

Result:
case a
α : Type u_1
inst✝⁴ : CancelCommMonoidWithZero α
inst✝³ : UniqueFactorizationMonoid α
inst✝² : DecidableEq (Associates α)
inst✝¹ : (p : Associates α) → Decidable (Irreducible p)
a p : Associates α
hp : Irreducible p
inst✝ : (n : ℕ) → Decidable (a ∣ p ^ n)
n : ℕ
h : a ∣ p ^ n
⊢ p ^ p.count a.factors = a