var subs = ["stones_sub", "other_sub", "about_sub"];

function toggle_sub(menu) {
	var vis = document.getElementById(menu).style.visibility;
	if(vis == "visible") {
		document.getElementById(menu).style.visibility = "hidden";
	}
	else {
		// first ensure other sub menus are hidden
		for(var i=0; i<subs.length; i++) {
			if(subs[i] != menu) {
				document.getElementById(subs[i]).style.visibility = "hidden";
			}
		}
		document.getElementById(menu).style.visibility = "visible";
	}
}