var n = 5;
var f = false;
var b = new Array;

function prel(){
   	if(document.images) {
	  for(i=1;i<=n;i++)
               {str = '/assets/images/formalization/' + i + '_a.jpg';
               b[i-1] = new Image();
               b[i-1].src = str;
}f = true;
 		}
}

function on(im){
	if (document.images && (f == true)) 
		{document.images[im].src="/assets/images/formalization/"+im+"_a.jpg";}
		
}
function off(im){
	if (document.images && (f == true))
		{document.images[im].src = "/assets/images/formalization/"+im+".jpg";}
}

function on_g(im){
	if (document.images && (f == true)) 
		{document.images[im].src="/assets/images/formalization/"+im+"_a.gif";}
		
}
function off_g(im){
	if (document.images && (f == true))
		{document.images[im].src = "/assets/images/formalization/"+im+".gif";}
}