On the Derived Length of Lie Solvable Group Algebras
On the Derived Length of Lie Solvable Group Algebras
On the Derived Length of Lie Solvable Group Algebras
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6 CHAPTER 1<br />
and for units a, b that<br />
[a, b] = ba (a, b) − 1 = (a −1 , b −1 ) − 1 ba.<br />
For <strong>the</strong> subsets X, Y ⊆ A we denote by [X, Y ] <strong>the</strong> additive subgroup<br />
generated by all <strong>Lie</strong> commutators [x, y] with x ∈ X and y ∈ Y . It is<br />
easy to check that<br />
X, Y = Y, X ,<br />
and<br />
for any X, Y, Z ⊆ A.<br />
[X, Y Z] ⊆ [X, Y ]Z + Y [X, Z]<br />
[XY, Z] ⊆ X[Y, Z] + [X, Z]Y,<br />
1.2.1 Series in <strong>the</strong> associated <strong>Lie</strong> algebra<br />
As before, let A be an associative algebra over <strong>the</strong> field F . Define<br />
<strong>the</strong> <strong>Lie</strong> derived series <strong>of</strong> A as follows: let δ [0] (A) = A and for n ≥ 0<br />
let<br />
δ [n+1] (A) = δ [n] (A), δ [n] (A) .<br />
Clearly,<br />
A = δ [0] (A) ⊇ δ [1] (A) ⊇ · · · ⊇ δ [m] (A) ⊇ · · · .<br />
We introduce similarly <strong>the</strong> strong <strong>Lie</strong> derived series <strong>of</strong> A: let<br />
δ (0) (A) = A and for n ≥ 0 let δ (n+1) (A) be <strong>the</strong> ideal <strong>of</strong> A generated by<br />
all <strong>Lie</strong> commutators [x, y] with x, y ∈ δ (n) (A), that is<br />
Evidently,<br />
δ (n+1) (A) = δ (n) (A), δ (n) (A) A.<br />
A = δ (0) (A) ⊇ δ (1) (A) ⊇ · · · ⊇ δ (m) (A) ⊇ · · · .<br />
It is easy to check that δ [n] (A) ⊆ δ (n) (A) for any n, but <strong>the</strong> equality<br />
does not always hold.<br />
We say that A is <strong>Lie</strong> solvable if <strong>the</strong>re exists m ∈ N such that<br />
δ [m] (A) = 0 and <strong>the</strong> number dlL(A) = min{m ∈ N | δ [m] (A) = 0} is