function change_visuel(div,position){
		if(document.getElementById(div).style.backgroundPosition!="center bottom" && document.getElementById(div).style.backgroundPosition!="50% bottom"){
			document.getElementById(div).style.backgroundPosition=position;
		}
	}
	
	function change_div(div){
		document.getElementById("div1").style.display = "none";
		document.getElementById("div2").style.display = "none";
		document.getElementById("div3").style.display = "none";
		document.getElementById("div4").style.display = "none";
		document.getElementById("lien1").style.backgroundPosition="top";
		document.getElementById("lien2").style.backgroundPosition="top";
		document.getElementById("lien3").style.backgroundPosition="top";
		document.getElementById("lien4").style.backgroundPosition="top";
		
		
		document.getElementById("div"+div).style.display = "";
		document.getElementById("lien"+div).style.backgroundPosition="center bottom";
	}