Operator algebra for Josephson tunneling

The operator algebra associated with Josephson tunneling is reexamined, with special attention given to the commutator of the pair current with the pair tunneling Hamiltonian. This commutator has been identified with the pair number operator, in the pseudoangular-momentum description. I find this identification to be erroneous. The commutator in question vanishes identically because of a symmetry in the underlying microscopic theory. Consequently the conventional Josephson-Anderson number-phase formalism provides a complete description of pair tunneling