  The crossed channels of generalized reaction \gamma N - \gamma N have been
considered. The transformation coefficients from the independent helicity
amplitudes to the invariant functions are calculated. The explicit expressions
for invariant functions have been obtained with the subject to the contribution
of Born diagrams in s-, u-, and t-channel and six resonances in s- and
u-channel. It has been shown that the obtained invariant functions meet the
requirements of crossing-symmetry.
