var old_id = '';
var is_opened  = 'none';

function toggle( id ) {

    id_obj = document.getElementById(id);
    is_opened = id_obj.style.display;

	if (id != 'a01')
	{
		document.getElementById('a01').style.display = 'none';
	}

    if (old_id != '' && is_opened == 'none') {
        old_id_obj = document.getElementById(old_id);
        old_id_obj.style.display = 'none';		
    }

    if (old_id != id || is_opened == 'none') {
        id_obj.style.display = 'block';
    }

    old_id = id;
}