D. M. Riley proved in [3] that, if A and B are either Lie nilpotent or Lie metabelian algebras, then their tensor product A ⊗ B is Lie soluble and obtained bounds on the Lie derived length of A ⊗ B. The aim of the present note is to improve Riley's bounds; moreover we consider also the cases in which A and B are either strongly Lie soluble or strongly Lie nilpotent algebras.
Mathematics Subject Classification (2000). 16R40.Keywords. Tensor product, Lie soluble algebras, Lie nilpotent algebras.1. Introduction. Throughout this note, by algebra we mean an associative algebra over a field F . Let R be an algebra. We consider the Lie algebra associated with R by setting [x, y] = xy − yx for all x, y ∈ R. As usual, for all subspaces V and W of R we denote by [V, W ] the subspace of R generated by the set of Lie commutators [x, y], with x ∈ V and y ∈ W . Moreover, we denote by V W the subspace of R generated by the set of products xy, where x ∈ V and y ∈ W . Put δ 0 (R) = R and define by induction δ n+1 (R) = [δ n (R), δ n (R)]. We say that R is Lie soluble if there exists an integer m such that δ m (R) = 0. The smallest integer with this property is called the Lie derived length of R and is denoted by dl L (R). In particular, R is said to be Lie metabelian if dl L (R) ≤ 2. Recall also that the Lie lower central chain of R is defined by γ 1 (R) = R and γ n+1 (R) = [γ n (R), R] and R is Lie nilpotent of class c if γ c+1 (R) = 0 and γ c (R) = 0. The integer c is called the Lie nilpotency class of R and is usually denoted by cl L (R).