  The off-cone Compton operator of twist-2 is Fourier transformed using a
general procedure which is applicable, in principle, to any QCD tensor operator
of definite (geometric) twist. That method allows, after taking the non-forward
matrix elements, to separate quite effectively their imaginary part and to
reveal some hidden structure in terms of appropriately defined variables,
including generalized Nachtmann variables. In this way, without using the
equations of motion, generalizations of the Wandzura-Wilzcek relation and of
the mass-corrected Callan-Gross relation to the non-forward scattering, having
the same shape as in the forward case, are obtained. In addition, new relations
for those structure functions which vanish in the forward case are derived.
These structure functions are written in terms of iterated generalized parton
distributions of $n$-th order.
