function showandlink(imgname)
{
  document.write ("<td align='center'><a href='javascript:show(\""+ imgname +"\")'><img src='graphics/"+ imgname +"-klein.jpg' /></a></td></td>")
}

function show(imgname)
{
  parent.body.document.write ("<img src='graphics/"+ imgname +"-groot.jpg' height='447' />")
}