var controllo;
function apri(URL, W, H)
{
if (controllo==1){POP.window.close();controllo=0};
X = (screen.width - W) / 2;
Y = (screen.height - H) / 2;
P = "width=" + W + ",height=" + H + ",";
P+= "top=" + Y + ",left=" + X + ",";
P+= "scrollbars=yes,status=no,resizable=no";
POP = window.open(URL, "", P);
POP.window.focus();
}