function toggle_visibility(id) {
	var e = document.getElementById(id);
	var ids=new Array('a1','a2','a3','a4','a5','a6','a7','a8','a9','a0','aa','ab','ac','ad','ae','af','ag','ah','ai','aj','ak','al','am','an','ao');
	for (var i=0;i<ids.length;i++){
		if (ids[i] == id) {
			// do nothing//
		document.getElementById(ids[i]).style.display = 'block';			
		}
		else {
		document.getElementById(ids[i]).style.display = 'none';			
		}
	}		  
//       if(e.style.display == 'none')
//          e.style.display = 'block';
}
//
//
function turnoff_visibility(id) {
		document.getElementById(id).style.display = 'none';			
}
function turnon_visibility(id) {
		document.getElementById(id).style.display = 'block';			
}