  Deligne proved that the weights of Siegel modular forms on any congruence
subgroup of the Siegel modular group of genus g>1 must be integral or half
integral. We give a different proof for this. It uses Mennicke's result that
subgroups of finite index of the Siegel modular group are congruence subgroups
and some techniques from a paper of Bass-Milnor-Serre.
