function toggle_submenu(to) {
	document.getElementById('menu_lessen').style.display = ((to)? 'block':'none');
	document.getElementById('lessen').style.backgroundColor = ((to)? '#ffffff':'');
	document.getElementById('lessen').style.color = ((to)? '#5cb4c0':'');
	document.getElementById('lessen').style.fontWeight = ((to)? 'bold':'');
}