  For a two layer system in a weak coupling BCS formalism any interlayer
interaction, regardless of its sign, enhances the critical temperature. The
sign has an effect upon the relative phase of the order parameter in each of
the two planes but not upon its magnitude. When one of the planes has a
dispersion consistent with CuO chains and no intrinsic pairing interaction
there is both an enhancement of the critical temperature and an s+d mixing in
both layers as the interlayer interaction is increased. The magnetic
penetration depth, c-axis Josephson tunneling, density of states and Knight
shift are calculated for several sets of model parameters.
