function survol_on(){
		document.getElementById("about").style.visibility ="visible";
		}
		
function survol_off(){
		document.getElementById("about").style.visibility ="hidden";
		}
		
function survol_on2(){
		document.getElementById("montreal").style.visibility ="visible";
		}
		
function survol_off2(){
		document.getElementById("montreal").style.visibility ="hidden";
		}