var visited = false;

function show_navigation( nav ){

	visited = true;	
	hide_navigation();
	document.getElementById("subnav_" + nav ).style.visibility = 'visible';
	visited = false;
}

function hide_navigation(){
	//alert ('visited = ' + visited );
	if( visited == true ){
		for(x=1; x<=5; x++){
			document.getElementById("subnav_" + x ).style.visibility = 'hidden';
		}
	}
}