© 2002 by London Mathematical Society
© The London Mathematical Society
Conjugation-Invariant Subspaces and Lie Ideals in Non-Selfadjoint Operator Algebras
Department of Mathematics, University of Alberta Edmonton, Alberta, Canada T6G 2G1, l.marcoux{at}ualberta.ca
Department of Mathematics and Statistics, University of Victoria Victoria, BC, Canada V8W 3P4, sourour{at}math.uvic.ca
Received 11 October 2000. Revision received 24 July 2001.
It is shown that a weakly closed subspace S of a nest algebra A is closed under conjugation by invertible elements in A, that is, a1Sa=S if and only if S is a Lie ideal. A similar result holds for not-necessarily-closed subspaces of algebras of infinite multiplicity. An explicit characterisation of weakly closed Lie ideals in a nest algebra is given.