anchor.diff:  function TActor.GetActive;  begin  result := _active end;
   function TActor.GetAlive;   begin  result := _alive end;
   
  -  
  +
    
   constructor TGroup.Create;
  
positive.code:     procedure Add( a : IActor );
      function Handle( msg : IMessage ):boolean; override;
    end;
  
    TMorph = class (TGroup, IMorph)
      bounds : Quad;
  
negative.code:   end;
    IMorph = interface (IGroup)
    end;
  
  const
    cmd_quit  =  -1;
    cmd_step  =  -2;
  