The Hermitian adjoint of a spherical tensor may be defined as ( T † † ) q ( k ) = ( − − 1 ) k − − q ( T − − q ( k ) ) † † . There is some arbitrariness in the choice of the phase factor: any factor containing (−1) will satisfy the commutation relations. The above choice of phase has the advantages of being real and that the tensor product of two commuting Hermitian operators is still Hermitian. Some authors define it with a different sign on q, without the k, or use only the floor of k.