One can also prove fundamental theorems for relativistic quantum field theories using the front form, including: (a) the cluster decomposition theorem and (b) the vanishing of the anomalous gravitomagnetic moment for any Fock state of a hadron; one also can show that a nonzero anomalous magnetic moment of a bound state requires nonzero angular momentum of the constituents. The cluster properties of light-front time-ordered perturbation theory, together with J z conservation, can be used to elegantly derive the Parke–Taylor rules for multi- gluon scattering amplitudes. The counting-rule behavior of structure functions at large x and Bloom–Gilman duality have also been derived in light-front QCD (LFQCD). The existence of "lensing effects" at leading twist, such as the T -odd "Sivers effect" in spin-dependent semi-inclusive deep-inelastic scattering, was first demonstrated using light-front methods.