window.addEvent('domready', function(){ 
		var totIncrement		= 0;
	  var increment			= 550;
	  var maxRightIncrement	= increment*(-2);
	  var fx = new Fx.Tween('myList', {
				property: 'margin-left',
				duration: 1000,
				transition: Fx.Transitions.Back.easeInOut,
				wait: true
	   });
	   
		//-------------------------------------
	  // EVENTS for the button "previous"
	  $('previous').addEvents({ 
          'click' : function(event){ 
		  if(totIncrement<0){
					totIncrement = totIncrement+increment;					
					fx.start(totIncrement);
				}
			}			  	  
      }); 
	 
       //-------------------------------------
	  // EVENTS for the button "next"
  	  $('next').addEvents({ 
					'click' : function(event){
			 	if(totIncrement>maxRightIncrement){
			 		totIncrement = totIncrement-increment;		    	
					fx.start(totIncrement);
				}
			}		  		  
      })
});