-- Mathlib/GroupTheory/Sylow.lean
theorem mapSurjective_surjective (p : ℕ) [Fact p.Prime] :
    Function.Surjective (Sylow.mapSurjective hf : Sylow p G → Sylow p G')

Proof state:
case h
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
hQ : ¬p ∣ Q.index
⊢ mapSurjective hf (hpQ.toSylow hQ) = P

Tactic:
rw [Sylow.ext_iff, Sylow.coe_mapSurjective, eq_comm]

Result:
case h
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
hQ : ¬p ∣ Q.index
⊢ ↑P = map f ↑(hpQ.toSylow hQ)

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
⊢ ∃ a, mapSurjective hf a = P

Tactic:
let Q₀ : Sylow p (P.comap f) := Sylow.nonempty.some

Result:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
⊢ ∃ a, mapSurjective hf a = P

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
⊢ ∃ a, mapSurjective hf a = P

Tactic:
have hPQ : Q.map f ≤ P := Subgroup.map_le_iff_le_comap.mpr (Subgroup.map_subtype_le Q₀.1)

Result:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
⊢ ∃ a, mapSurjective hf a = P

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
⊢ ¬p ∣ (↑Q₀).index * (↑P).index

Tactic:
exact Nat.Prime.not_dvd_mul Fact.out Q₀.not_dvd_index P.not_dvd_index

Result:
no goals

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
⊢ Function.Surjective (mapSurjective hf)

Tactic:
intro P

Result:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
⊢ ∃ a, mapSurjective hf a = P

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
⊢ ∃ a, mapSurjective hf a = P

Tactic:
let Q : Subgroup G := Q₀.map (P.comap f).subtype

Result:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
⊢ ∃ a, mapSurjective hf a = P

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
⊢ ∃ a, mapSurjective hf a = P

Tactic:
have hQ : ¬ p ∣ Q.index := by
  rw [Subgroup.index_map_subtype Q₀.1, P.index_comap_of_surjective hf]
  exact Nat.Prime.not_dvd_mul Fact.out Q₀.not_dvd_index P.not_dvd_index

Result:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
hQ : ¬p ∣ Q.index
⊢ ∃ a, mapSurjective hf a = P

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
hQ : ¬p ∣ Q.index
⊢ ∃ a, mapSurjective hf a = P

Tactic:
use hpQ.toSylow hQ

Result:
case h
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
hQ : ¬p ∣ Q.index
⊢ mapSurjective hf (hpQ.toSylow hQ) = P

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
⊢ ∃ a, mapSurjective hf a = P

Tactic:
have hpQ : IsPGroup p Q := Q₀.2.map (P.comap f).subtype

Result:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
⊢ ∃ a, mapSurjective hf a = P

Proof state:
case h
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
hQ : ¬p ∣ Q.index
⊢ ↑P = map f ↑(hpQ.toSylow hQ)

Tactic:
exact ((hpQ.map f).toSylow (fun h ↦ hQ (h.trans (Q.index_map_dvd hf)))).3 P.2 hPQ

Result:
no goals

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
⊢ ¬p ∣ Q.index

Tactic:
rw [Subgroup.index_map_subtype Q₀.1, P.index_comap_of_surjective hf]

Result:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
P : Sylow p G'
Q₀ : Sylow p ↥(comap f ↑P) := ⋯.some
Q : Subgroup G := map (comap f ↑P).subtype ↑Q₀
hPQ : map f Q ≤ ↑P
hpQ : IsPGroup p ↥Q
⊢ ¬p ∣ (↑Q₀).index * (↑P).index

Proof state:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
⊢ Function.Surjective (mapSurjective hf)

Tactic:
have : Finite G' := Finite.of_surjective f hf

Result:
G : Type u_1
inst✝³ : Group G
inst✝² : Finite G
G' : Type u_2
inst✝¹ : Group G'
f : G →* G'
hf : Function.Surjective ⇑f
p : ℕ
inst✝ : Fact (Nat.Prime p)
this : Finite G'
⊢ Function.Surjective (mapSurjective hf)