-- Mathlib/Algebra/Lie/Solvable.lean
theorem derivedSeries_of_derivedLength_succ (I : LieIdeal R L) (k : ℕ) :
    derivedLengthOfIdeal R L I = k + 1 ↔
      IsLieAbelian (derivedSeriesOfIdeal R L k I) ∧ derivedSeriesOfIdeal R L k I ≠ ⊥

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : k₁ ∈ s
⊢ derivedSeriesOfIdeal R L k₂ I ≤ ⊥

Tactic:
change derivedSeriesOfIdeal R L k₁ I = ⊥ at h₁

Result:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : derivedSeriesOfIdeal R L k₁ I = ⊥
⊢ derivedSeriesOfIdeal R L k₂ I ≤ ⊥

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : k₁ ∈ s
this : derivedSeriesOfIdeal R L k₂ I ≤ ⊥
⊢ k₂ ∈ s

Tactic:
exact eq_bot_iff.mpr this

Result:
no goals

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
⊢ ∀ (k₁ k₂ : ℕ), k₁ ≤ k₂ → k₁ ∈ s → k₂ ∈ s

Tactic:
intro k₁ k₂ h₁₂ h₁

Result:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : k₁ ∈ s
⊢ k₂ ∈ s

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
⊢ derivedLengthOfIdeal R L I = k + 1 ↔ derivedSeriesOfIdeal R L (k + 1) I = ⊥ ∧ derivedSeriesOfIdeal R L k I ≠ ⊥

Tactic:
change sInf s = k + 1 ↔ k + 1 ∈ s ∧ k ∉ s

Result:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
⊢ sInf s = k + 1 ↔ k + 1 ∈ s ∧ k ∉ s

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : derivedSeriesOfIdeal R L k₁ I = ⊥
⊢ derivedSeriesOfIdeal R L k₂ I ≤ ⊥

Tactic:
rw [← h₁]

Result:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : derivedSeriesOfIdeal R L k₁ I = ⊥
⊢ derivedSeriesOfIdeal R L k₂ I ≤ derivedSeriesOfIdeal R L k₁ I

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : k₁ ∈ s
⊢ k₂ ∈ s

Tactic:
suffices derivedSeriesOfIdeal R L k₂ I ≤ ⊥ by exact eq_bot_iff.mpr this

Result:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : k₁ ∈ s
⊢ derivedSeriesOfIdeal R L k₂ I ≤ ⊥

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
⊢ derivedLengthOfIdeal R L I = k + 1 ↔ IsLieAbelian ↥(derivedSeriesOfIdeal R L k I) ∧ derivedSeriesOfIdeal R L k I ≠ ⊥

Tactic:
rw [abelian_iff_derived_succ_eq_bot]

Result:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
⊢ derivedLengthOfIdeal R L I = k + 1 ↔ derivedSeriesOfIdeal R L (k + 1) I = ⊥ ∧ derivedSeriesOfIdeal R L k I ≠ ⊥

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
⊢ sInf s = k + 1 ↔ k + 1 ∈ s ∧ k ∉ s

Tactic:
have hs : ∀ k₁ k₂ : ℕ, k₁ ≤ k₂ → k₁ ∈ s → k₂ ∈ s := by
  intro k₁ k₂ h₁₂ h₁
  suffices derivedSeriesOfIdeal R L k₂ I ≤ ⊥ by exact eq_bot_iff.mpr this
  change derivedSeriesOfIdeal R L k₁ I = ⊥ at h₁; rw [← h₁]
  exact derivedSeriesOfIdeal_antitone I h₁₂

Result:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
hs : ∀ (k₁ k₂ : ℕ), k₁ ≤ k₂ → k₁ ∈ s → k₂ ∈ s
⊢ sInf s = k + 1 ↔ k + 1 ∈ s ∧ k ∉ s

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
hs : ∀ (k₁ k₂ : ℕ), k₁ ≤ k₂ → k₁ ∈ s → k₂ ∈ s
⊢ sInf s = k + 1 ↔ k + 1 ∈ s ∧ k ∉ s

Tactic:
exact Nat.sInf_upward_closed_eq_succ_iff hs k

Result:
no goals

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
k₁ k₂ : ℕ
h₁₂ : k₁ ≤ k₂
h₁ : derivedSeriesOfIdeal R L k₁ I = ⊥
⊢ derivedSeriesOfIdeal R L k₂ I ≤ derivedSeriesOfIdeal R L k₁ I

Tactic:
exact derivedSeriesOfIdeal_antitone I h₁₂

Result:
no goals

Proof state:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
⊢ derivedLengthOfIdeal R L I = k + 1 ↔ derivedSeriesOfIdeal R L (k + 1) I = ⊥ ∧ derivedSeriesOfIdeal R L k I ≠ ⊥

Tactic:
let s := { k | derivedSeriesOfIdeal R L k I = ⊥ }

Result:
R : Type u
L : Type v
inst✝² : CommRing R
inst✝¹ : LieRing L
inst✝ : LieAlgebra R L
I : LieIdeal R L
k : ℕ
s : Set ℕ := {k | derivedSeriesOfIdeal R L k I = ⊥}
⊢ derivedLengthOfIdeal R L I = k + 1 ↔ derivedSeriesOfIdeal R L (k + 1) I = ⊥ ∧ derivedSeriesOfIdeal R L k I ≠ ⊥