  In contrast with the recent photoemission observations by Shen et al. of
anomalous temperature-induced momentum-dependent spectral weight transfer in
Bi_2Sr_2CaCu_2O_{8+delta}, we find that in the same material, in spite of the
unusual spectral lineshape change between superconducting and normal states,
the integrated spectral weight displays minimum variation as a function of
temperature, which is in agreement with the sum rule of angle-resolved
photoemission: the integrated spectral weight is proportional to the momentum
density, n(k).
