  In this paper, we extend our previous result from [16]. We prove that
transport equations with rough coefficients do possess a uniqueness property.
Our method relies strongly on duality and bears a strong resemblance with the
well-known DiPerna-Lions theory first developed in [8]. As an application, we
show a uniqueness result for the Euler and Navier-Stokes equations at the Leray
regularity scale. In turn, this theorem stands as a barrier against the
paradoxical weak solutions constructed in [17], [18], [19] and later
reformulated in [6].
