function visible(zone) {
    if (document.layers) {
        document.layers[zone].visibility = 'show';
    }
    else if (document.all) {
        document.all[zone].style.visibility = 'visible';
    }
    else if (document.getElementById) {
        document.getElementById(zone).style.visibility = 'visible';

    }
}
function invisible(zone) {
    if (document.layers) {
        document.layers[zone].visibility = 'hide';
    }
    else if (document.all) {
        document.all[zone].style.visibility = 'hidden';
    }
    else if (document.getElementById) {
        document.getElementById(zone).style.visibility = 'hidden';
    }
}