  Conformal blocks for the WZW model on tori can be represented by vector
valued Weyl anti-symmetric theta functions on the Cartan subalgebra satisfying
vanishing conditions on root hyperplanes. We introduce a quantum version of
these vanishing conditions in the sl(2) case. They are compatible with the qKZB
equations and are obeyed by the hypergeometric solutions as well as by their
critical level counterpart, which are Bethe eigenfunctions of IRF row-to-row
transfer matrices. In the language of IRF models the vanishing conditions turn
out to be equivalent to the sl(2) fusion rules defining restricted models.
