Relative completions of linear groups over Z[t] and Z[t,t^{-1}]
  We compute the completion of the groups SL_n(Z[t]) and SL_n(Z[t,t^{-1}]) relative to the obvious homomorphisms to SL_n(Q); this is a generalization of the classical Malcev completion. We also make partial computations of the rational second cohomology of these groups. 
Kevin P. Knudson (Northwestern University)