-- Mathlib/GroupTheory/OrderOfElement.lean
lemma charP_of_ne_zero (hn : card R = p) (hR : ∀ i < p, (i : R) = 0 → i = 0) : CharP R p where
  cast_eq_zero_iff' n

Proof state:
case mpr.intro
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
H : ↑p = 0
n : ℕ
⊢ ↑(p * n) = 0

Tactic:
rw [Nat.cast_mul, H, zero_mul]

Result:
no goals

Proof state:
case mp
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑n = 0
⊢ p ∣ n

Tactic:
rw [← Nat.mod_add_div n p, Nat.cast_add, Nat.cast_mul, H, zero_mul, add_zero] at h

Result:
case mp
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑(n % p) = 0
⊢ p ∣ n

Proof state:
case mpr
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
⊢ p ∣ n → ↑n = 0

Tactic:
rintro ⟨n, rfl⟩

Result:
case mpr.intro
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
H : ↑p = 0
n : ℕ
⊢ ↑(p * n) = 0

Proof state:
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑(n % p) = 0
⊢ Nonempty R

Tactic:
exact ⟨0⟩

Result:
no goals

Proof state:
case mp
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑(n % p) = 0
⊢ n % p = 0

Tactic:
apply hR _ (Nat.mod_lt _ _) h

Result:
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑(n % p) = 0
⊢ p > 0

Proof state:
case mp
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
⊢ ↑n = 0 → p ∣ n

Tactic:
intro h

Result:
case mp
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑n = 0
⊢ p ∣ n

Proof state:
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
⊢ ↑p = 0

Tactic:
rw [← hn, Nat.cast_card_eq_zero]

Result:
no goals

Proof state:
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
⊢ ↑n = 0 ↔ p ∣ n

Tactic:
constructor

Result:
case mp
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
⊢ ↑n = 0 → p ∣ n

case mpr
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
⊢ p ∣ n → ↑n = 0

Proof state:
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑(n % p) = 0
⊢ p > 0

Tactic:
rw [← hn, gt_iff_lt, Fintype.card_pos_iff]

Result:
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑(n % p) = 0
⊢ Nonempty R

Proof state:
case mp
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑(n % p) = 0
⊢ p ∣ n

Tactic:
rw [Nat.dvd_iff_mod_eq_zero]

Result:
case mp
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
h : ↑(n % p) = 0
⊢ n % p = 0

Proof state:
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
⊢ ↑n = 0 ↔ p ∣ n

Tactic:
have H : (p : R) = 0 := by rw [← hn, Nat.cast_card_eq_zero]

Result:
R : Type u_6
inst✝¹ : NonAssocRing R
p : ℕ
inst✝ : Fintype R
hn : card R = p
hR : ∀ i < p, ↑i = 0 → i = 0
n : ℕ
H : ↑p = 0
⊢ ↑n = 0 ↔ p ∣ n