  A brief introduction is given in the generic microscopic framework of
superconductivity. The consequences for the temperature dependence of the
kinetic energy, and the correlation energy are discussed for two cases: The BCS
scenario and the non-Fermi liquid scenario. A quantitative comparison is made
between the BCS-prediction for d-wave pairing in a band with nearest neighbor
and next-nearest neighbor hoppping and the experimental specific heat and the
optical intraband spectral weight along the plane. We show that the
BCS-prediction produces the wrong sign for the kink at Tc of the intraband
spectral weight, even though the model calculation agrees well with the
specific heat.
