function change(id) {
   // loop through all divs
   var divs= document.getElementsByTagName('div');
   // looks through the divs collected for
   // class 'visible' and sets to 'invisible'
   for (i=0 ; i<divs.length ; i++) {
      if (divs[i].className=='visible') {
         divs[i].className='invisible';
      }
   }
   // set clicked div id to visible
   identity=document.getElementById(id);
   identity.className='visible';
}