-- 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
⊢ p ∣ #(filter (fun a_1 => ↑x a_1 ≠ 0) univ)

Tactic:
rw [← CharP.cast_eq_zero_iff (ZMod p), ← Finset.sum_boole]

Result:
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

Proof state:
case intro.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
⊢ ∑ i ∈ Finset.map { toFun := Subtype.val, inj' := ⋯ } (filter (fun a_1 => ↑x a_1 ≠ 0) univ), a i = 0

Tactic:
simpa [f₂, ZMod.pow_card_sub_one, Finset.sum_filter] using x.2.2

Result:
no goals

Proof state:
case intro.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
⊢ #(Finset.map { toFun := Subtype.val, inj' := ⋯ } (filter (fun a_1 => ↑x a_1 ≠ 0) univ)) = p

Tactic:
rw [card_map]

Result:
case intro.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
⊢ #(filter (fun a_1 => ↑x a_1 ≠ 0) univ) = p

Proof state:
case intro.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
⊢ Finset.map { toFun := Subtype.val, inj' := ⋯ } (filter (fun a_1 => ↑x a_1 ≠ 0) univ) ⊆ s

Tactic:
simp +contextual [subset_iff]

Result:
no goals

Proof state:
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

Tactic:
refine ⟨({a | x.1 a ≠ 0} : Finset _).map ⟨(↑), Subtype.val_injective⟩, ?_, ?_, ?_⟩

Result:
case intro.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
⊢ Finset.map { toFun := Subtype.val, inj' := ⋯ } (filter (fun a_1 => ↑x a_1 ≠ 0) univ) ⊆ s

case intro.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
⊢ #(Finset.map { toFun := Subtype.val, inj' := ⋯ } (filter (fun a_1 => ↑x a_1 ≠ 0) univ)) = p

case intro.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
⊢ ∑ i ∈ Finset.map { toFun := Subtype.val, inj' := ⋯ } (filter (fun a_1 => ↑x a_1 ≠ 0) univ), 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 }
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

Tactic:
have hN₀ : 0 < N := @Fintype.card_pos _ _ ⟨zero_sol⟩

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
⊢ ∃ 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 }
zero_sol : { x // (eval x) (f₁ s a) = 0 ∧ (eval x) (f₂ s a) = 0 } := ⟨0, ⋯⟩
hN₀ : 0 < N
⊢ 2 * p - 1 = Fintype.card { x // x ∈ s }

Tactic:
simp [hs]

Result:
no goals

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
⊢ 2 * p - 1 < 2 * p

Tactic:
exact tsub_lt_self (mul_pos zero_lt_two (Fact.out : p.Prime).pos) zero_lt_one

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
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0

Tactic:
haveI : NeZero p := inferInstance

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
⊢ ∃ t ⊆ s, #t = p ∧ ∑ i ∈ t, a i = 0