Abstract. Let R be a semiprime ring with a derivation d and let U be a Lie ideal of R, a ∈ R. Suppose that ad(u) n = 0 for all u ∈ U, where n is a fixed positive integer. Then ad(I) = 0 for I the ideal of R generated by [U, U ] and if R is 2-torsion free, then ad(U ) = 0. Furthermore, R is a subdirect sum of semiprime homomorphic images R 1 and R 2 with derivations d 1 and d 2 , induced canonically by d, respectively such that ad 1 (R 1 ) = 0 and the image of U in R 2 is commutative (central if R is 2-torsion free), where a denotes the image of a in R 1 . Moreover, if U = R, then ad(R) = 0. This gives Bresar's theorem without the (n − 1)!-torsion free assumption on R.
In [8] I. N. Herstein proved that if R is a prime ring and d is an inner derivation of R such that d(x)n = 0 for all x ∈ R and n a fixed integer, then d = 0. In [6] A. Giambruno and I. N. Herstein extended this result to arbitrary derivations in semiprime rings. In [2] L. Carini and A. Giambruno proved that if R is a prime ring with a derivation d such that d (x) n(x) = 0 for all x ∈ U, a Lie ideal of R, then d(U ) = 0 when R has no nonzero nil right ideals, char R = 2 and the same conclusion holds when n(x) = n is fixed and R is a 2-torsion free semiprime ring. Using the ideas in [2] and the methods in [5] C. Lanski [11] removed both the bound on the indices of nilpotence and the characteristic assumptions on R.In [1] M. Bresar gave a generalization of the result due to I. N. Herstein and A. Giambruno [6] in another direction. Explicitly, he proved the theorem: Let R be a semiprime ring with a derivation d, a ∈ R. If ad(x) n = 0 for all x ∈ R, where n is a fixed integer, then ad(R) = 0 when R is an (n − 1)!-torsion free ring. The present paper is then motivated by Bresar's result and by Lanski's paper [11]. We prove Bresar's result without the assumption of (n − 1)!-torsion free on R. In fact, we study the Lie ideal case as given in [11] and then obtain Bresar's result as the corollary to our main result. More precisely, we shall prove the following Main Theorem. Let R be a semiprime ring with a derivation d and let U be a Lie ideal of R, a ∈ R. Suppose that ad(u) n = 0 for all u ∈ U , where n is a fixed integer. Then ad(I) = 0 for I the ideal of R generated by [U, U ] and if R is 2-torsion free, then ad(U ) = 0.Furthermore, R is a subdirect sum of semiprime homomorphic images R 1 and R 2 with derivations d 1 and d 2 , induced canonically by d, respectively such that