Derivations with large separating subspace

Abstract

In his famous paper The image of a derivation is contained in the radical, Marc Thomas establishes the (commutative) Singer-Wermer conjecture, showing that derivations from a commutative Banach algebra A to itself must map into the radical. The proof goes via first showing that the separating subspace of a derivation on A must lie in the radical of A. In this paper, we exhibit discontinuous derivations on a commutative unital Frechet algebra A such that the separating subspace is the whole of A. Thus, the situation on Frechet algebras is markedly different from that on Banach algebras.