###
Alan Robinson: `Obstruction theory for E_{infty}
ring structures'.

There are some four different (equivalent) definitions of the gamma
(co)homology of a commutative ring. I describe how one of them is a
bicomplex which arises naturally when one sets up an obstruction theory
for putting an E_{infty} structure on a ring spectrum E (with
E_{*}E flat over E_{*}, and the Künneth and universal
coefficient theorems holding for E_{*}-theory). Proofs can
be sketched.