  We investigate existence and uniqueness of duality solutions for a scalar
conservation law with a nonlocal interaction kernel. Following the work of
Bouchut and James (Comm. Partial Diff. Eq., 24, 1999), a notion of duality
solution for such a nonlinear system is proposed, for which we do not have
uniqueness. Then we prove that a natural definition of the flux allows to
select a solution for which uniqueness holds.
