var lev_1 = new Image();
var lev_2 = new Image();
var prav_1 = new Image();
var prav_2 = new Image();
function preload()
{
	lev_1.src = "images/lev_1.gif";
	lev_2.src = "images/lev_2.gif";
	prav_1.src = "images/prav_1.gif";
	prav_2.src = "images/prav_2.gif";
}

function onButton1(image)
{
	var img = document.images[image];
	if(img.src.indexOf('lev_1.gif') >= 0) img.src = lev_2.src;
	else img.src = lev_1.src;
}

function onButton2(image)
{
	var img = document.images[image];
	if(img.src.indexOf('prav_1.gif') >= 0) img.src = prav_2.src;
	else img.src = prav_1.src;
}