function switchlayer(Layer_Name)
{
  var GECKO = document.getElementById? 1:0 ;
  var NS = document.layers? 1:0 ;
  var IE = document.all? 1:0 ;
disable();
  if (GECKO)
       {document.getElementById(Layer_Name).style.display=
	   (document.getElementById(Layer_Name).style.display=='block') ? 'none' : 'block';}
  else if (NS)
       {document.layers[Layer_Name].display=(document.layers[Layer_Name].display==
	   'block') ? 'none' : 'block';}
  else if (IE)
       {document.all[Layer_Name].style.display=(document.all[Layer_Name].style.display==
	   'block') ? 'none' : 'block';}
}
function disable() {

  var GECKO = document.getElementById? 1:0 ;
  var NS = document.layers? 1:0 ;
  var IE = document.all? 1:0 ;

  if (GECKO)
       {document.getElementById('bl_1').style.display= 'none';
        document.getElementById('bl_2').style.display= 'none';
        document.getElementById('bl_3').style.display= 'none';
        document.getElementById('bl_4').style.display= 'none';
        document.getElementById('bl_r').style.display= 'none';        
        document.getElementById('bl_f').style.display= 'none';
        document.getElementById('bl_f2').style.display= 'none';        
        document.getElementById('bl_p').style.display= 'none';
        document.getElementById('f3').style.display= 'none';        
       }
  else if (NS)
       {document.layers['bl_1'].display='none';
       document.layers['bl_2'].display='none';
       document.layers['bl_3'].display='none';
       document.layers['bl_4'].display='none';
       document.layers['bl_r'].display='none';
       document.layers['bl_f'].display='none';
       document.layers['bl_f2'].display='none';       
       document.layers['bl_p'].display='none';       
       document.layers['f3'].display='none';       
       }
  else if (IE)
       {document.all['bl_1'].style.display='none' ;
       document.all['bl_2'].style.display='none' ;
       document.all['bl_3'].style.display='none' ;
       document.all['bl_4'].style.display='none' ;       
       document.all['bl_r'].style.display='none' ;       
       document.all['bl_f'].style.display='none' ;       
       document.all['bl_f2'].style.display='none' ;       
       document.all['bl_p'].style.display='none' ;
       document.all['f3'].style.display='none' ;       
       }
}