Theorem: least_descending_central_series_length_eq_nilpotencyClass
File: Mathlib/GroupTheory/Nilpotent.lean

tactic: rw [← least_ascending_central_series_length_eq_nilpotencyClass]
state_before: G : Type u_1
inst✝¹ : Group G
H : Subgroup G
inst✝ : Normal H
hG : Group.IsNilpotent G
⊢ Nat.find (_ : ∃ n H, IsDescendingCentralSeries H ∧ H n = ⊥) = nilpotencyClass G

tactic: refine le_antisymm (Nat.find_mono ?_) (Nat.find_mono ?_)
state_before: G : Type u_1
inst✝¹ : Group G
H : Subgroup G
inst✝ : Normal H
hG : Group.IsNilpotent G
⊢ Nat.find (_ : ∃ n H, IsDescendingCentralSeries H ∧ H n = ⊥) =
    Nat.find (_ : ∃ n H, IsAscendingCentralSeries H ∧ H n = ⊤)

tactic: rintro n ⟨H, ⟨hH, hn⟩⟩
state_before: case refine_1
G : Type u_1
inst✝¹ : Group G
H : Subgroup G
inst✝ : Normal H
hG : Group.IsNilpotent G
⊢ ∀ (n : ℕ), (∃ H, IsAscendingCentralSeries H ∧ H n = ⊤) → ∃ H, IsDescendingCentralSeries H ∧ H n = ⊥

tactic: refine ⟨fun m => H (n - m), is_decending_rev_series_of_is_ascending G hn hH, ?_⟩
state_before: case refine_1.intro.intro
G : Type u_1
inst✝¹ : Group G
H✝ : Subgroup G
inst✝ : Normal H✝
hG : Group.IsNilpotent G
n : ℕ
H : ℕ → Subgroup G
hH : IsAscendingCentralSeries H
hn : H n = ⊤
⊢ ∃ H, IsDescendingCentralSeries H ∧ H n = ⊥

tactic: dsimp only
state_before: case refine_1.intro.intro
G : Type u_1
inst✝¹ : Group G
H✝ : Subgroup G
inst✝ : Normal H✝
hG : Group.IsNilpotent G
n : ℕ
H : ℕ → Subgroup G
hH : IsAscendingCentralSeries H
hn : H n = ⊤
⊢ (fun m => H (n - m)) n = ⊥

tactic: rw [tsub_self]
state_before: case refine_1.intro.intro
G : Type u_1
inst✝¹ : Group G
H✝ : Subgroup G
inst✝ : Normal H✝
hG : Group.IsNilpotent G
n : ℕ
H : ℕ → Subgroup G
hH : IsAscendingCentralSeries H
hn : H n = ⊤
⊢ H (n - n) = ⊥

tactic: exact hH.1
state_before: case refine_1.intro.intro
G : Type u_1
inst✝¹ : Group G
H✝ : Subgroup G
inst✝ : Normal H✝
hG : Group.IsNilpotent G
n : ℕ
H : ℕ → Subgroup G
hH : IsAscendingCentralSeries H
hn : H n = ⊤
⊢ H 0 = ⊥

tactic: rintro n ⟨H, ⟨hH, hn⟩⟩
state_before: case refine_2
G : Type u_1
inst✝¹ : Group G
H : Subgroup G
inst✝ : Normal H
hG : Group.IsNilpotent G
⊢ ∀ (n : ℕ), (∃ H, IsDescendingCentralSeries H ∧ H n = ⊥) → ∃ H, IsAscendingCentralSeries H ∧ H n = ⊤

tactic: refine ⟨fun m => H (n - m), is_ascending_rev_series_of_is_descending G hn hH, ?_⟩
state_before: case refine_2.intro.intro
G : Type u_1
inst✝¹ : Group G
H✝ : Subgroup G
inst✝ : Normal H✝
hG : Group.IsNilpotent G
n : ℕ
H : ℕ → Subgroup G
hH : IsDescendingCentralSeries H
hn : H n = ⊥
⊢ ∃ H, IsAscendingCentralSeries H ∧ H n = ⊤

tactic: dsimp only
state_before: case refine_2.intro.intro
G : Type u_1
inst✝¹ : Group G
H✝ : Subgroup G
inst✝ : Normal H✝
hG : Group.IsNilpotent G
n : ℕ
H : ℕ → Subgroup G
hH : IsDescendingCentralSeries H
hn : H n = ⊥
⊢ (fun m => H (n - m)) n = ⊤

tactic: rw [tsub_self]
state_before: case refine_2.intro.intro
G : Type u_1
inst✝¹ : Group G
H✝ : Subgroup G
inst✝ : Normal H✝
hG : Group.IsNilpotent G
n : ℕ
H : ℕ → Subgroup G
hH : IsDescendingCentralSeries H
hn : H n = ⊥
⊢ H (n - n) = ⊤

tactic: exact hH.1
state_before: case refine_2.intro.intro
G : Type u_1
inst✝¹ : Group G
H✝ : Subgroup G
inst✝ : Normal H✝
hG : Group.IsNilpotent G
n : ℕ
H : ℕ → Subgroup G
hH : IsDescendingCentralSeries H
hn : H n = ⊥
⊢ H 0 = ⊤