function newImage(arg) {
	if (document.images) {
		rslt = new Image();
		rslt.src = arg;
		return rslt;
	}
}

function changeImages() {
	if (document.images && (preloadFlag == true)) {
		for (var i=0; i<changeImages.arguments.length; i+=2) {
			document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
		}
	}
}

var preloadFlag = false;
function preloadImages() {
	if (document.images) {
		internal_10_over = newImage("images/internal_10-over.jpg");
		internal_11_over = newImage("images/internal_11-over.jpg");
		internal_13_over = newImage("images/internal_13-over.jpg");
		internal_15_over = newImage("images/internal_15-over.jpg");
		internal_16_over = newImage("images/internal_16-over.jpg");
		internal_17_over = newImage("images/internal_17-over.jpg");
		learn_sub_01_over = newImage("images/learn_sub_01-over.gif");
		learn_sub_02_over = newImage("images/learn_sub_02-over.gif");
		learn_sub_03_over = newImage("images/learn_sub_03-over.gif");
		preloadFlag = true;
	}
}