function next(x)
{
var prev=x-1;
document.getElementById('page_'+x).style.display='block';
document.getElementById('page_'+prev).style.display='none';
}

function previous(x)
{
var prev=x-1;
document.getElementById('page_'+x).style.display='none';
document.getElementById('page_'+prev).style.display='block';
}