function show_div(div_id) {
    // hide all the divs
	hide_div();

    // show the requested div
    document.getElementById(div_id).style.display = 'block';
}
function hide_div() {
    // hide all the divs
    document.getElementById('the_div_1').style.display = 'none';
    document.getElementById('the_div_2').style.display = 'none';
    document.getElementById('the_div_3').style.display = 'none';
    document.getElementById('the_div_4').style.display = 'none';
    document.getElementById('the_div_5').style.display = 'none';
    document.getElementById('the_div_6').style.display = 'none';
    document.getElementById('the_div_7').style.display = 'none';
}