function $ (name) {
    return document.getElementById(name);
}

window.onload = function () {
    var z0 = $('z0');
    var z2 = $('z2');
    var drag = Draggable.attachedTo(z2);
    var p;

    drag.ondragbegin = function () {
	p = Point.fromElementLayout(z2);
    };

    drag.ondragmotion = function (delta) {
	var offset = delta.add(p);
	offset.toStyleOf(z2);
	offset.toStyleOf(z0);
    };

};