function findObj(id) { //v4.0
    if (document.all) {
        return document.all[id];
    }
    else if (document.getElementById) {
        return document.getElementById(id);
    }
    else if (document.layers) {
        return document.layers[id];
    }
}

function changestyle(couche, style) {
    var layer = findObj(couche);
	layer.style.visibility = style;
}