Grothendieck duality theory assigns to essentially-finite-type maps f of noetherian schemes a pseudofunctor f× right-adjoint to Rf∗, and a pseudofunctor f ! agreeing with f× when f is proper, but equal to the usual inverse image f∗ when f is étale. We define and study a canonical map from the first pseudofunctor to the second. This map behaves well with respect to flat base change, and is taken...