/*! @page mandatories LEmuSR Tree

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\anchor mandatory
@section smandatories The mandatory classes

The simplest Geant4 simulation requires four so-called mandatory classes. These classes provide the main information about the simulation fundamental parameters, like the detector description or the physical interaction taken in account. They are initialized at the beginning of LEMuSR.cc:

<UL>
<LI>@ref runmgr : it is the Geant4 mandatory class used to initialize the kernel.
</LI>
<LI>@ref geometry : mandatory user <b>initialization</b> class for the detector geometry. The geometry is mainly defined in the LEMuSRDetectorConstruction files.
</LI>
<LI>@ref physicsref : mandatory user <b>initialization </b>class for the physical interactions. The file LEMuSRPhysicsList registers the different particle interaction classes, defined separately, as for example LEMuSRMuonPhysics.
</LI>
<LI>@ref pga : mandatory user <b>action</b> class for the simulation monitoring. All the initial parameters of the muon beam are described in the file LEMuSRPrimaryGeneratorAction
</LI>
</UL> 
  */