Sum rule for deep-inelastic electroproduction from polarized protons

A sum rule is derived for the asymmetry in deep-inelastic scattering of polarized electrons from polarized protons: $\int 0^{1}d\xi g^{\mathrm{ep}}\left(\xi \right)\approx 0.15g_A$. The result follows from the quark light-cone algebra and the assumption that strange quarks do not contribute to the asymmetry. The latter is justified by conventional parton-model arguments.