Subject: Re: categories: Query on bisimplicial groups. Date: Thu, 4 Apr 2002 14:34:16 -0500 (EST) From: Michael Barr I am not familiar with the Artin-Mazur codiagonal, but Jon Beck once showed me a proof (unpublished like most of his work) that the geometric realization of the diagonal and of the whole thing were homotopic. The geometric realization of the whole thing was a coend of X_{ij} x \Delta_i x \Delta_j. The proof of the homology is much easier and will appear in my forthcoming Acyclic Models. On Thu, 4 Apr 2002, Prof. T.Porter wrote: > Dear all, > > It is folklore that for a bisimplicial group $X_{*,*}$ the diagonal and > the Artin Mazur `codiagonal' construction have the same homotopy type. > > Can anyone point me to a published proof? > > > Thanks, > > Tim Porter > > >