function layer(id){
  var res
  if(document.getElementById) res=document.getElementById(id)
  if(document.all) res=document.all[id]
  if (res) return res.style
  return null
}

function t_i(id) {
	var hlp=layer('H'+id)
	if(hlp) hlp.visibility='visible'
}
function t_o(id) {
	var hlp=layer('H'+id)
	if(hlp) hlp.visibility='hidden'
}