  We present a compact form of the leptonic currents for the computation of the
processes involving an initial virtual boson (photon, $W^{\pm}$ or $Z_0$). For
deeply inelastic scattering, once the azimuthal angle of the plane expanded by
the initial- and final-state leptons are integrated over in the boson-proton
rest frame, the azimuthal-asymmetric terms vanish, which, however, is NOT true
when some physical quantities (such as the transverse momentum of the observed
particle) are specified in laboratory frame. The abuse of the symmetry may lead
to wrong results.
