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## Preliminary vocabulary

Before going any further, we should femiliarize ourselves with some basic vocabulary. In this report we will encounter some words taken from C++ language, and others related to Geant4 architecture. Let us have a brief description of them.

1. C++ words
     Class: a class is the definition of a collection of variables or functions called the members of the class. For example the class Particle has for members: mass, lifetime, charge ...In other words, the class defines a type of variable with parameters that can be specified.
     Instance, object: in order to use a class in a program one may create an instance, or object, of it. For example Particle particle1 will create a variable of the type Particle. It is then possible to set all the parameters of the object particle1 and to use it independently in the program.
     Inheritance: it is possible to build subclasses. For example, Lepton would be a subclass of Particle class. Instead of building a totally new class, one just have to give Lepton class all the caracteristics of a Particle and add the properties which make a particle a muon. We say that Lepton class inherits from Particle class.
2. Gean4 words
     Run: this is the word for a the simulation process.
     Event: during a run, one can shoot as many particles as needed. An event is the simulation of all the primary particles. Before the run the user specifies the number of primary particles shoot per Event as well as the number of events.
     Track: this is the information collection of one particle tracking
     Step: step by step, a track is build. At each step the simulation engine is called to decide the process that the particle will suffer, this in accordance to cross-sections or priority orders defined by the user.

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