-- Mathlib/Combinatorics/Additive/ErdosGinzburgZiv.lean
theorem ZMod.erdos_ginzburg_ziv_prime (a : ι → ZMod p) (hs : #s = 2 * p - 1) :
    ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Proof state:
case intro.refine_2.refine_2
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
hpN : p ∣ N
x : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
hx : x ≠ zero_sol
⊢ (∑ x_1 : { x // x ∈ s }, if ↑x x_1 ≠ 0 then 1 else 0) = 0

Tactic:
simpa only [f₁, map_sum, ZMod.pow_card_sub_one, map_pow, eval_X] using x.2.1

Result:
no goals

Proof state:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
⊢ (eval 0) (f₁ s a) = 0 ∧ (eval 0) (f₂ s a) = 0

Tactic:
simp [f₁, f₂, map_sum, (Fact.out : p.Prime).one_lt, tsub_eq_zero_iff_le]

Result:
no goals

Proof state:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
hpN : p ∣ N
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Tactic:
obtain ⟨x, hx⟩ := Fintype.exists_ne_of_one_lt_card ((Fact.out : p.Prime).one_lt.trans_le <|
  Nat.le_of_dvd hN₀ hpN) zero_sol

Result:
case intro
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
hpN : p ∣ N
x : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
hx : x ≠ zero_sol
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Proof state:
case intro.refine_2.refine_1
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
hpN : p ∣ N
x : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
hx : x ≠ zero_sol
⊢ (filter (fun a_1 => ↑x a_1 ≠ 0) univ).Nonempty

Tactic:
rw [← Subtype.coe_ne_coe, Function.ne_iff] at hx

Result:
case intro.refine_2.refine_1
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
hpN : p ∣ N
x : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
hx : ∃ a_1, ↑x a_1 ≠ ↑zero_sol a_1
⊢ (filter (fun a_1 => ↑x a_1 ≠ 0) univ).Nonempty

Proof state:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Tactic:
have hs' : 2 * p - 1 = Fintype.card s := by simp [hs]

Result:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Proof state:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Tactic:
let zero_sol : {x // eval x (f₁ s a) = 0 ∧ eval x (f₂ s a) = 0} :=
  ⟨0, by simp [f₁, f₂, map_sum, (Fact.out : p.Prime).one_lt, tsub_eq_zero_iff_le]⟩

Result:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Proof state:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Tactic:
set N := Fintype.card {x // eval x (f₁ s a) = 0 ∧ eval x (f₂ s a) = 0}

Result:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Proof state:
case intro.refine_2.refine_3
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
hpN : p ∣ N
x : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
hx : x ≠ zero_sol
⊢ #univ < 2 * p

Tactic:
rw [univ_eq_attach, card_attach, hs]

Result:
case intro.refine_2.refine_3
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
hpN : p ∣ N
x : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
hx : x ≠ zero_sol
⊢ 2 * p - 1 < 2 * p

Proof state:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Tactic:
have hpN : p ∣ N := char_dvd_card_solutions_of_add_lt p
  (totalDegree_f₁_add_totalDegree_f₂.trans_eq hs')

Result:
ι : Type u_1
p : ℕ
inst✝ : Fact (Nat.Prime p)
s : Finset ι
a : ι → ZMod p
hs : #s = 2 * p - 1
this : NeZero p
N : ℕ := Fintype.card { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
hs' : 2 * p - 1 = Fintype.card { x // x ∈ s }
hpN : p ∣ N
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0