On Lie nilpotent rings and Cohen's Theorem

We study certain (two-sided) nil ideals and nilpotent ideals in a Lie nilpotent ring R. Our results lead us to showing that the prime radical rad® of R comprises the nilpotent elements of R, and that if L is a left ideal of R, then L+rad® is a two-sided ideal of R. This in turn leads to a Lie nilpotent version of Cohen’s theorem, namely if R is a Lie nilpotent ring and every prime (two-sided) ideal of R is finitely generated as a left ideal, then every left ideal of R containing the prime radical of R is finitely generated (as a left ideal). For an arbitrary ring R with identity we also consider its so-called n-th Lie center Z_n®, which is a Lie nilpotent ring of index n. We prove that if C is a commutative submonoid of the multiplicative monoid of R, then the subring of R generated by the union of Z_n® and C is also Lie nilpotent of index n.