A file found in a source-path can not have more than one externally visible definitio

[lookup]

package {
	import flash.display.Sprite;
	import flash.events.Event;
 
	public class bubbles extends Sprite
	{
		var bubble : Bubble ;
		public function bubbles()
		{
			bubble = new Bubble();
			addEventListener(Event.ENTER_FRAME,onEnterFrame);
		}
		public function onEnterFrame(event:Event){
			bubble.y++;
		}
	}
 
	class Bubble extends Sprite{
		public function Bubble(){
			graphics.lineStyle(1,0,1);
			graphics.beginFill(0x000000,1);
			graphics.drawCircle(100,0);
			graphics.endFill();
			addChild(this);
		}
	}
}

Вот как избавиться от ошибки?