  Being reformulated in the color dipole basis of small-x QCD Adler's theorem
establishes a connection between perturbative and non-perturbative descriptions
of DIS and quantifies the effect of non-perturbative dynamics on
would-be-perturbative observables. In particular, it provides a quantitative
measure of the non-perturbative influence on the longitudinal structure
function in charged current DIS and imposes stringent constraints on
non-perturbative parameters of color dipole models. Our analysis calls for new
experimental tests of Adler's theorem in diffractive neutrino scattering.
