Lie isomorphisms of reflexive algebras

A Lie isomorphism phi between algebras is called trivial if phi = psi + tau, where psi is an (algebraic) isomorphism or a negative of an (algebraic) anti-isomorphism, and tau is a linear map with image in the center vanishing on each commutator. In this paper, we investigate the conditions for the triviality of Lie isomorphisms from reflexive algebras with completely distributive and commutative lattices (CDCSL). In particular, we prove that a Lie isomorphism between irreducible CDCSL algebras is trivial if and only if it preserves I-idempotent operators (the sum of an idempotent and a scalar multiple of the identity) in both directions. We also prove the triviality of each Lie isomorphism from a CDCSL algebra onto a CSL algebra which has a comparable invariant projection with rank and corank not one. Some examples of Lie isomorphisms are presented to show the sharpness of the conditions. (C) 2006 Elsevier Inc. All rights reserved.