function next( element_prefix, element_id ) {

    div_current = document.getElementById( element_prefix + element_id );
    div_next = document.getElementById( element_prefix + (element_id+1) );

    div_current.style.display = 'none';
    div_next.style.display = 'inline';
}
function previous( element_prefix, element_id ) {

    div_previous = document.getElementById( element_prefix + (element_id-1) );
    div_current = document.getElementById( element_prefix + element_id );

    div_current.style.display = 'none';
    div_previous.style.display = 'inline';
}

function show_and_hide( element_prefix, element_id_to_show, element_id_to_hide ) {

    div_to_hide = document.getElementById( element_prefix + element_id_to_hide );
    div_to_show = document.getElementById( element_prefix + element_id_to_show );

    div_to_hide.style.display = 'none';
    div_to_show.style.display = 'inline';
}