  Using the Sudakov technique we sum the perturbation series for the process
$3\to 3$ and obtain the compact analytical expression for the amplitude of this
process, which takes into account all possible Coulomb interactions between
colliding particles. Compare it with the amplitude of the lepton pair
production in heavy ion collision i.e. in the process $ 2\to 4$, we show that
crossing symmetry between this processes holds only if one neglects the
interaction of produced pair with ions (i.e. in the approximation
$Z_{1,2}\alpha \ll 1$).
