  The theory of exact C*-algebras was introduced by Kirchberg and has been
influential in recent development of C*-algebras. A fundamental result on exact
C*-algebras is a local characterization of exactness. The notion of weakly
exact von Neumann algebras was also introduced by Kirchberg. In this paper, we
give a local characterization of weak exactness. As a corollary, we prove that
a discrete group is exact if and only if its group von Neumann algebra is
weakly exact. The proof naturally involves the operator space duality.
