window.addEvent('domready', function(){ 
	  var increment = 0;
	  var fx = new Fx.Style('myList', 'margin-left', {
				duration: 1000,
				transition: Fx.Transitions.Back.easeInOut,
				wait: true
	   });
	  $('previous').addEvents({ 
          'click' : function(event){ 
		  	increment = increment +212;
		    fx.stop()
			fx.start(increment);
          }		  		  
      }); 
  
  	  $('next').addEvents({ 
          'click' : function(event){ 
		  	increment = increment -212;
		    fx.stop()
			fx.start(increment);
          }		  		  
      })
});