  This paper presents a complete description of the interaction of two solitons
with nearly equal speeds for the quartic (gKdV) equation. By constructing an
approximate solution of the problem, we prove that at the main order, the two
solitons are preserved by the interaction and that for all time they are
separated by a large distance, as in the case of the integrable KdV equation in
this regime. However, unlike in the integrable case, we prove that the
collision is not perfectly elastic.
