The problem of classifying semigroups of endomorphisms of type [italic]I[subscript]infinity symbol factors to outer conjugacy is reduced to the problem of classifying certain simpler structures associated to them, called product systems. Product systems are intimately connected with continuous tensor products of Hilbert spaces. We develop the general theory of product systems and give a number of applications to semigroups of endomorphisms of von Neumann algebras; in particular, we introduce a numerical invariant for such semigroups which is analogous to the Fredholm index.
The problem of classifying semigroups of endomorphisms of type [italic]I[subscript]infinity symbol factors to outer conjugacy is reduced to the problem of classifying certain simpler structures associated to them, called product systems. Product systems are intimately connected with continuous te...