function show_(div_id) {

    show   = 'show-'    + div_id;
    div_id = 'content-' + div_id;

    // hide the show
    document.getElementById(show).style.visibility = 'hidden';

    // show the requested div
    document.getElementById(div_id).style.display = 'block';
}
function hide_(div_id) {

    show   = 'show-'    + div_id;
    div_id = 'content-' + div_id;
	
    // show the show
    document.getElementById(show).style.visibility = 'visible';

    // hide the requested div
    document.getElementById(div_id).style.display = 'none';
}