function roll(what){c1=document.images[what].src.substring(0,document.images[what].src.length-4); c2=document.images[what].src.substring(document.images[what].src.length-4,document.images[what].src.length); document.images[what].src=c1+'_over'+c2;}
function unroll(what){c1=document.images[what].src.substring(0,document.images[what].src.length-9); c2=document.images[what].src.substring(document.images[what].src.length-4,document.images[what].src.length); document.images[what].src=c1+c2;}