English
The equality of underlying sets of derived series holds consistently when passing from R to ℤ, i.e., the coefficients do not affect the set-theoretic realization of the derived series.
Русский
Эквивалентность множества производящих серий при переходе от кольца R к целым ℤ сохраняется на уровне множеств.
LaTeX
$$$(\mathrm{derivedSeries} \ R \ L \ k : Set L) = (\mathrm{derivedSeries} \ ℤ \ L \ k : Set L)$$$
Lean4
instance isSolvableAdd {I J : LieIdeal R L} [IsSolvable I] [IsSolvable J] : IsSolvable (I + J) :=
by
obtain ⟨k, hk⟩ := IsSolvable.solvable R I
obtain ⟨l, hl⟩ := IsSolvable.solvable R J
exact IsSolvable.mk (LieIdeal.derivedSeries_add_eq_bot hk hl)