Tensor operators and Wigner-Eckart theorem for U_q->0(sl(2))
  Crystal tensor operators, which tranform under U_q->0(sl(2)), in analogous way as the vectors of the crystal basis, are introduced. The Wigner-Eckart theorem for the crystal tensor is defined: the selection rules depend on the initial state and on the component of the tensor operator; the transition amplitudes to the states of the same final irreducible representation are all equal. 
Vincenzo Marotta and Antonino Sciarrino