  We compaWe compare the absorptive corrections to the one pion exchange in
$pp\to Xn$ and $ep\to e'Xn$ reactions. It is shown that the absorption is
stronger in the case of $pp$ collision. The difference in strength of the
absorption for the $pp\to Xn$ and $ep\to e'Xn$ reactions breaks the
factorization peculiar to the pure one pion exchange. We evaluate the emerging
model dependence of extraction of the small-$x$ pion structure function from an
analysis of the HERA data on the neutron production at physical values of $t$.
