function roll(img_name, img_src)  {document[img_name].src = img_src;}

function show(elementIdName){
	var NAME = document.getElementById(elementIdName) 
	var cssStyle = "navshow";
	NAME.className = cssStyle;
}

function hide(elementIdName){
	var NAME = document.getElementById(elementIdName) 
	var cssStyle = "navhide";
	NAME.className = cssStyle;
}