function clip (id) {
if (document.getElementById("span_" + id).style.display == 'none') {
document.getElementById("img_" + id).src = "symbols/minus.gif";
document.getElementById("span_" + id).style.display = "block"; }
else {
document.getElementById("img_" + id).src = "symbols/plus.gif";
document.getElementById("span_" + id).style.display = "none"; } }