function fold(nr) {
    if (document.layers) {
        current = document.layers[nr].display == "none" ? "block" : "none";
        document.layers[nr].display = current;
    } else if (document.all) {
        current = document.all[nr].style.display == "none" ? "block" : "none";
        document.all[nr].style.display = current;
    } else if (document.getElementById) {
        vista = document.getElementById(nr).style.display == "block" ? "none" : "block";
        document.getElementById(nr).style.display = vista;
    }
}