ABSTRACT
As a tool kit, Geant4 provides a set of libraries, a main function, and a family of initialization and action classes to be implemented by the user. These classes are singlets, and their associated objects are constructed in main. The objects contain the information related to the geometry of the apparatus, the fields, the beam, and actions taken by the user at different times during the simulation. The Geant4 library classes start with the G4 prefix. The example described in this section, called MuCool, uses only some of the many available user classes.
