
               **************
               ***  DEMO  ***
               **************

 Visualize the different events for:
   geantino, chargedgeantino, mu-, e-, pi- 
 and create a simple gui which allows the selection
 of: particle gun, energy, number of events for few, 
 common possible choices.

 --- MAIN : some additions are necessary...
     Use the precompiler 
            #ifdef G4UI_USE_XM
            ...
            #endif

 --- A macro file  gui.g4  should be used.


 NB) In the display, the following colours are used:
        * green : neutral particles (mainly gammas and neutrons);
        * blue  : positive charged particles 
        * red   : negative charged particles
     In MyEventAction, by default all particles produced, 
     of all momenta, are displayed. Because the neutral ones
     (gammas and neutrons) are dominant in the display 
     (they can have a sizeable path length in the matter),
     display only the charged ones.



