function turnOn(id) {
	var booknav = document.getElementById("booknav");
	var spreads = booknav.getElementsByTagName("a");
	spreads[id].setAttribute("id","selected");
	var book = document.getElementById("book");
	book.setAttribute("src",bookspread[id]);
	}
	
function turnOff() {
	var booknav = document.getElementById("booknav");
	var spreads = booknav.getElementsByTagName("a");
	for (var i = 0; i < spreads.length; i++) {
		var status = spreads[i].getAttribute("id");
			if (status == "selected") {
				spreads[i].setAttribute("id","");
			}
		}
	}
	
function toggle(id) {
	turnOff();
	turnOn(id);
}