 The noncontroversial operational core of quantum theory consists of rules for identifying, for any given system, appropriate operators representing its dynamical quantities. In addition, there are prescriptions for evolving the state of system when it is acted upon by specified external fields or subjected to various manipulations (see  section 1.3).  Application of quantum theory typically involves a distinction between the system under study, which is treated quantum mechanically, and experimental apparatus, which is not. This division is sometimes known as the Heisenberg cut.