  It is shown that, based only upon two empirically known facts besides two
reasonable theoretical postulates, we are inevitably led to a model-independent
conclusion that the quark orbital angular momentum carries nearly half of the
total nucleon spin at the low energy scale of nonperturbative QCD. Also shown
are explicit model predictions for the forward limit of the unpolarized
spin-flip GPDs, which are believed to give valuable information on the
distributions of quark angular momentum inside the nucleon.
