var VisibleLink = '';
    var iVisible = 0;
    
     function collapse(id) { 
          if (document.getElementById('laag_'+id).style.display=='none') {
              document.getElementById('laag_'+id).style.display='';
              document.getElementById('laag_'+id).style.visibility='visible';

              if (iVisible != -1) {                        
                  if (document.getElementById('laag_'+iVisible)) {
	                  document.getElementById('laag_'+iVisible).style.display='none';
   	               document.getElementById('laag_'+iVisible).style.visibility='hidden';
						}
              }
              iVisible = id;
           } else {    
               document.getElementById('laag_'+id).style.display='none';
               document.getElementById('laag_'+id).style.visibility='hidden';
               iVisible = -1;
           }
    }