function  display(str)
   { 
	 document.getElementById('link1').style.visibility="hidden"
	 document.getElementById('link1').style.display="none"
	 document.getElementById('link2').style.visibility="hidden"
	 document.getElementById('link2').style.display="none"
	 document.getElementById('link3').style.visibility="hidden"
	 document.getElementById('link3').style.display="none"
	 document.getElementById('link4').style.visibility="hidden"
	 document.getElementById('link4').style.display="none"
	 document.getElementById('link5').style.visibility="hidden"
	 document.getElementById('link5').style.display="none"
	 document.getElementById('link6').style.visibility="hidden"
	 document.getElementById('link6').style.display="none"

	 document.getElementById(str).style.visibility="visible"
	 document.getElementById(str).style.display="block"
  }