function vrstva(jm1) {

  var dom = document.getElementById ? true : false; 
  var ie4 = ((document.all) && (!dom)) ? true : false;
  var ns4 = document.layers ? true : false;
  var opera = navigator.userAgent.indexOf('Opera') != -1 ? true : false;
  var dhtml = dom ? true : ie4 ? true : ns4 ? true : false; 
  
  if(ns4) {
   document.layers['a'].visibility="hidden";
   document.layers['b'].visibility="hidden";
   document.layers['c'].visibility="hidden";
   document.layers['d'].visibility="hidden";
   document.layers['e'].visibility="hidden";
	 document.layers['x'].visibility="hidden";
   document.layers[jm1].visibility="show";   }
  else {
   document.getElementById('a').style.visibility="hidden";
   document.getElementById('b').style.visibility="hidden";
   document.getElementById('c').style.visibility="hidden";
   document.getElementById('d').style.visibility="hidden";
   document.getElementById('e').style.visibility="hidden";
	 document.getElementById('x').style.visibility="hidden";
   document.getElementById(jm1).style.visibility="visible"; }}