Now let ψ ψ be any of the eigenstates of B ^ ^ , which are given by ψ ψ ( θ θ ) = e 2 π π i n θ θ . These states are normalizable, unlike the eigenstates of the momentum operator on the line. Also the operator A ^ ^ is bounded, since θ θ ranges over a bounded interval. Thus, in the state ψ ψ , the uncertainty of B is zero and the uncertainty of A is finite, so that σ σ A σ σ B = 0. The Robertson uncertainty principle does not apply in this case: ψ ψ is not in the domain of the operator B ^ ^ A ^ ^ , since multiplication by θ θ disrupts the periodic boundary conditions imposed on B ^ ^ .