var sections_hidden = Array();
sections_hidden['teaching'] = false;

function get_element(id) {
    var e;

    if (document.getElementById) {
	// DOM3 = IE5, NS6
	e = document.getElementById(id);
    } else {
	if (document.layers) {
            // Netscape 4
            e = document.id;
	} else {
            // IE 4
            e = document.all.id;
	}
    }

    return e;
}
      
function flip_element(id, hide) {
    var s, e;

    if (hide)
	s = 'none';
    else
	s = 'block';

    e = get_element(id);
    if (!e) return;

    if (document.getElementById) {
	// DOM3 = IE5, NS6
	e.style.display = s;
    } else {
	if (document.layers) {
            // Netscape 4
            e.display = s;
	} else {
            // IE 4
            e.style.display = s;
	}
    }
}

function show_and_hide(n)
{
    var img_id, img_src, img_element;

    flip_element(n, !sections_hidden[n]);

    img_id = "menubox_" + n;
    img_element = get_element(img_id);
    if (img_element) {
	if (sections_hidden[n])
	    img_src = "images/menu_open.png";
	else
	    img_src = "images/menu_close.png";

	if (document.getElementById) {
	    // DOM3 = IE5, NS6
	    img_element.src = img_src;
	} else {
	    if (document.layers) {
		// Netscape 4
		img_element.src = img_src;
	    } else {
		// IE 4
		img_element.src = img_src;
	    }
	}
    }

    sections_hidden[n] = !sections_hidden[n];
}