English
For a solvable ideal I, derivedAbelianOfIdeal(I) equals zero iff I equals zero; otherwise it is nonzero.
Русский
Для разрешимого идеала I: derivedAbelianOfIdeal(I)=0 тогда и только тогда, когда I=0; иначе ненулевой.
LaTeX
$$$\mathrm{derivedAbelianOfIdeal}(I) = 0 \iff I=0.$$$
Lean4
theorem abelian_of_solvable_ideal_eq_bot_iff (I : LieIdeal R L) [h : IsSolvable I] :
derivedAbelianOfIdeal I = ⊥ ↔ I = ⊥ :=
by
dsimp only [derivedAbelianOfIdeal]
split
· simp_all only [derivedLength_zero]
· rename_i k h
obtain ⟨_, h₂⟩ := (derivedSeries_of_derivedLength_succ R L I k).mp h
have h₃ : I ≠ ⊥ := by rintro rfl; apply h₂; apply derivedSeries_of_bot_eq_bot
simp only [h₂, h₃]