Published online by Cambridge University Press: 01 January 1999
In this paper we study the cohomology groups Hn(I, I*) and Hn([Uscr ], [Uscr ]*) where [Uscr ] is a Banach algebra with a bounded approximate identity and I is a codimension one closed two-sided ideal of [Uscr ]. This is applied to the case when [Uscr ] is the group algebra L1(G) of a locally compact group G and I={f∈L1(G)[mid ] ∫Gf=0}, the augmentation ideal of G. We show that if G is inner amenable, then I is always weakly amenable, i.e. [Hscr ]1(I, I*)={0}.