  We discuss the role of nucleon and its excited state poles in the twist
expansion of the nucleon structure function moments. We find that the nucleon
pole contribution was overestimated in previous analyses by a factor of two.
Inclusion of this missing factor makes the duality appear for all moments at
least down to Q2=1 GeV2. For resonance poles the time reversal invariance
together with unitarity demand at least four of them in the forward Compton
scattering amplitude. These poles as well as the elastic pole can be propagated
separately through the standard Operator Product Expansion derivation for DIS.
This part of the amplitude gives a coherent, positive, higher twist
contribution, which can be singled out of the total and compared with the
remaining one given mostly by threshold effects. A comparison of the estimated
resonance contribution to the data on structure function moments allows to test
large-Q2 behavior of proton-resonance transition form-factors.
