function hideX(n) {
var x = document.getElementById(n);
if (x.style.display == "block") {
	x.style.display = "none";
} else {
	x.style.display = "block";
}
var y = document.getElementById('img'+n) ;
if (y.alt == "expand") {
	y.src = "/multimedia/images/img_structures/collapse_.gif" ; //le lien vers l'image
	y.alt = "collapse" ;   //la balise alt
} else{
	y.src = "/multimedia/images/img_structures/expand_.gif" ;
	y.alt = "expand" ;
}
}