AS2. while loop, setInterval, clearInterval problem

[dawsonk]

on (release) {
	clearInterval(myInterval);
	var myInterval = setInterval(slow, 33);
	var counter = 0;
	function slow() {
		if (counter<20) {
			counter++;
			trace(counter);
			trace("slow function");
			prevFrame();
		} else {
			clearInterval(myInterval);
			trace("clear interval");
		}
	}
}