function showHide(layerName){ // shows and hides a given layer 
		     if (document.getElementById){ 
		          //alert('ns7'); 
		          var fred = document.getElementById(layerName); 
		          var display = fred.style.display ? '' : 'none'; 
		          fred.style.display = display; 
		          return; 
		     } 
		} 
		 
		function showLayer(layerName){ // shows a given layer 
		     if (document.getElementById){ 
		          var fred = document.getElementById(layerName); 
		          if(fred){ 
		               var display = fred.style.display = ''; 
		               fred.style.display = display; 
		               return; 
		          } 
		     } 
		} 
		 
		function hideLayer(layerName){ // hides a given layer 
		     if (document.getElementById){ 
		          var fred = document.getElementById(layerName); 
		          var display = fred.style.display = 'none'; 
		          fred.style.display = display; 
		          return; 
		     } 
		}