function side_nav_show(id)
{
  document.getElementById('t-'+id+'_l').className = "nav";
  document.getElementById('t-'+id+'_r').className = "nav";
}

function side_nav_hide(id)
{
  document.getElementById('t-'+id+'_l').className = "nav_invisible";
  document.getElementById('t-'+id+'_r').className = "nav_invisible";
}