var plusImg = new Image();
plusImg.src ="img/books.gif"
var minusImg = new Image();
minusImg.src ="img/books_on.gif"

function hideLevel( _levelId, _imgId ) {
var thisLevel = document.getElementById( _levelId );
var thisImg = document.getElementById( _imgId );
thisLevel.style.display = 'none';
thisImg.src = plusImg.src;
}

function showLevel( _levelId, _imgId ) {
var thisLevel = document.getElementById( _levelId );
var thisImg = document.getElementById( _imgId );
if (thisLevel.style.display == 'none') {
thisLevel.style.display = 'block';
thisImg.src = minusImg.src;
}
else {
hideLevel( _levelId, _imgId );
}
}

function hideAll() {
hideLevel('l1','aa');
hideLevel('l2','bb');
hideLevel('l3','cc');
hideLevel('l4','dd');
hideLevel('l5','ee');
hideLevel('l6','ff');
hideLevel('l7','gg');
}

var xmlhttp = false;
try {
	xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
	try {
		xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
	} catch (E) {
		xmlhttp = false;
	}
}
if (!xmlhttp && typeof XMLHttpRequest != 'undefined') {
	xmlhttp = new XMLHttpRequest();
}

function makerequest(serverPage, objID) {
	
	var obj = document.getElementById(objID);
	xmlhttp.open("GET", serverPage);
	xmlhttp.onreadystatechange = function() {
		if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
			obj.innerHTML = xmlhttp.responseText;
		}
	}
	xmlhttp.send(null);
}