function vorschau() {
	here = location.href;
	str_pos = here.lastIndexOf(".html");
	yea = parseInt(here.substring(str_pos-6,str_pos-2));
	mon = parseInt(here.substring(str_pos-2,str_pos),10);//alert(mon)
	if(mon == 12) { 
		yea += 1;
		mon = "01";
	}
	else {
			mon += 1;
			if (mon < 10) {
			mon = "0" + mon;
		}
	}
	dateiname='prog'+ yea + mon + '.html'; //alert(dateiname);
	window.location = dateiname;
}

function rueckschau() {
	here = location.href;
	str_pos = here.lastIndexOf(".html");
	yea = parseInt(here.substring(str_pos-6,str_pos-2));
	mon = parseInt(here.substring(str_pos-2,str_pos),10);//alert(mon)
	if(mon == 01) { 
		yea -= 1;
		mon = "12";
	}
	else {
			mon -= 1;
			if (mon < 10) {
			mon = "0" + mon;
		}
	}
	dateiname='prog'+ yea + mon + '.html'; //alert(dateiname);
	window.location = dateiname;
}