Alan Robinson: `Obstruction theory for Einfty 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 Einfty 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.