Subsystems of Fock Need Not Be Fock: Spatial CP-Semigroups
  We show that a product subsystem of a time ordered system (that is, a product system of time ordered Fock modules), though type I, need not be isomorphic to a time ordered product system. In that way, we answer an open problem in the classification of CP-semigroups by product systems. We define spatial strongly continuous CP-semigroups on a unital C*-algebra and characterize them as those that have a Christensen-Evans generator. 
B.V.Rajarama Bhat, Volkmar Liebscher, Michael Skeide