Theorem: alternatingGroup.isPreprimitive_of_stabilizer_lt
Proof state before:
case a.left
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
s : Set α
h0 : Set.Nontrivial s
h1 : Set.Nontrivial sᶜ
hα : Set.ncard s < Set.ncard sᶜ
h4 : 4 ≤ Fintype.card α
G : Subgroup (Equiv.Perm α)
hG : stabilizer (Equiv.Perm α) s ⊓ alternatingGroup α < G ⊓ alternatingGroup α
this : IsPretransitive (↥G) α
hB_ne_sc : ∀ (B : Set α), IsBlock (↥G) B → ¬B = sᶜ
hB_not_le_sc : ∀ (B : Set α), IsBlock (↥G) B → B ⊆ sᶜ → Set.Subsingleton B
hB_not_le_s : ∀ (B : Set α), IsBlock (↥G) B → B ⊆ s → Set.Subsingleton B
B : Set α
hB : IsBlock (↥G) B
hB' : ¬Set.Subsingleton B
a : α
ha : a ∈ B
ha' : a ∈ s
b : α
hb : b ∈ B
hb' : b ∈ sᶜ
x : α
hx' : x ∈ sᶜ
k : ↥(alternatingGroup α)
hk : k ∈ fixingSubgroup (↥(alternatingGroup α)) s
hkbx : k • b = x
⊢ ↑k ∈ stabilizer (Equiv.Perm α) s

case a.right
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
s : Set α
h0 : Set.Nontrivial s
h1 : Set.Nontrivial sᶜ
hα : Set.ncard s < Set.ncard sᶜ
h4 : 4 ≤ Fintype.card α
G : Subgroup (Equiv.Perm α)
hG : stabilizer (Equiv.Perm α) s ⊓ alternatingGroup α < G ⊓ alternatingGroup α
this : IsPretransitive (↥G) α
hB_ne_sc : ∀ (B : Set α), IsBlock (↥G) B → ¬B = sᶜ
hB_not_le_sc : ∀ (B : Set α), IsBlock (↥G) B → B ⊆ sᶜ → Set.Subsingleton B
hB_not_le_s : ∀ (B : Set α), IsBlock (↥G) B → B ⊆ s → Set.Subsingleton B
B : Set α
hB : IsBlock (↥G) B
hB' : ¬Set.Subsingleton B
a : α
ha : a ∈ B
ha' : a ∈ s
b : α
hb : b ∈ B
hb' : b ∈ sᶜ
x : α
hx' : x ∈ sᶜ
k : ↥(alternatingGroup α)
hk : k ∈ fixingSubgroup (↥(alternatingGroup α)) s
hkbx : k • b = x
⊢ ↑k ∈ alternatingGroup α
Tactic:
suffices hk' : k ∈ stabilizer (alternatingGroup α) s by
  simpa [mem_stabilizer_iff] using hk'
Proof state after:
case a.left
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
s : Set α
h0 : Set.Nontrivial s
h1 : Set.Nontrivial sᶜ
hα : Set.ncard s < Set.ncard sᶜ
h4 : 4 ≤ Fintype.card α
G : Subgroup (Equiv.Perm α)
hG : stabilizer (Equiv.Perm α) s ⊓ alternatingGroup α < G ⊓ alternatingGroup α
this : IsPretransitive (↥G) α
hB_ne_sc : ∀ (B : Set α), IsBlock (↥G) B → ¬B = sᶜ
hB_not_le_sc : ∀ (B : Set α), IsBlock (↥G) B → B ⊆ sᶜ → Set.Subsingleton B
hB_not_le_s : ∀ (B : Set α), IsBlock (↥G) B → B ⊆ s → Set.Subsingleton B
B : Set α
hB : IsBlock (↥G) B
hB' : ¬Set.Subsingleton B
a : α
ha : a ∈ B
ha' : a ∈ s
b : α
hb : b ∈ B
hb' : b ∈ sᶜ
x : α
hx' : x ∈ sᶜ
k : ↥(alternatingGroup α)
hk : k ∈ fixingSubgroup (↥(alternatingGroup α)) s
hkbx : k • b = x
⊢ k ∈ stabilizer (↥(alternatingGroup α)) s

case a.right
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
s : Set α
h0 : Set.Nontrivial s
h1 : Set.Nontrivial sᶜ
hα : Set.ncard s < Set.ncard sᶜ
h4 : 4 ≤ Fintype.card α
G : Subgroup (Equiv.Perm α)
hG : stabilizer (Equiv.Perm α) s ⊓ alternatingGroup α < G ⊓ alternatingGroup α
this : IsPretransitive (↥G) α
hB_ne_sc : ∀ (B : Set α), IsBlock (↥G) B → ¬B = sᶜ
hB_not_le_sc : ∀ (B : Set α), IsBlock (↥G) B → B ⊆ sᶜ → Set.Subsingleton B
hB_not_le_s : ∀ (B : Set α), IsBlock (↥G) B → B ⊆ s → Set.Subsingleton B
B : Set α
hB : IsBlock (↥G) B
hB' : ¬Set.Subsingleton B
a : α
ha : a ∈ B
ha' : a ∈ s
b : α
hb : b ∈ B
hb' : b ∈ sᶜ
x : α
hx' : x ∈ sᶜ
k : ↥(alternatingGroup α)
hk : k ∈ fixingSubgroup (↥(alternatingGroup α)) s
hkbx : k • b = x
⊢ ↑k ∈ alternatingGroup α