  Rings form a bicategory [Rings], with classes of bimodules as horizontal
arrows, and bimodule maps as vertical arrows. The notion of Morita equivalence
for rings can be translated in terms of bicategories in the following way. Two
rings are Morita equivalent if and only if they are isomorphic objects in the
bicategory. We repeat this construction for von Neumann algebras. Von Neumann
algebras form a bicategory [W*], with classes of correspondences as horizontal
arrows, and intertwiners as vertical arrows. Two von Neumann algebras are
Morita equivalent if and only if they are isomorphic objects in the bicategory
[W*].
