class a {
	function a() {
		if(!isset($GLOBALS["b"])) {
			echo "loading b";
			$GLOBALS["b"] = new b();
		}
	}
}
class b {
	function b() {
		if(!isset($GLOBALS["a"])) {
			echo "loading a";
			$GLOBALS["a"] = new a();
		}
	}
}
# creates an infinite loop
new a();