function shownav(which) {
	var nav_basename = "thumbnails_";
	var nav_count = 0;
	while ($(nav_basename+(nav_count+1)) != null) {
    nav_count++;
	}
	//close other nav items
	for (i=1;i<=nav_count;i++) {
    $(nav_basename+i).style.display = "none";
	}
	$('thumbnails_'+which).style.display = "block";
}

function hidenav() {
	var nav_basename = "thumbnails_";
	var nav_count = 0;
	while ($(nav_basename+(nav_count+1)) != null) {
    nav_count++;
	}
	//close other nav items
	for (i=1;i<=nav_count;i++) {
    $(nav_basename+i).style.display = "none";
	}
}