public static void tryInit(ServletContext sc) {
        if (OK) {
            return;
        }
        final String fmt = "/index/uliss18_%s";
        int i = 0;
        streams = new ArrayList<>();
        InputStream is = sc.getResourceAsStream(String.format(fmt, i));
        while (is != null) {
            streams.add(is);
            is = sc.getResourceAsStream(String.format(fmt, ++i));
        }
        instance = new InvertedIndex();
        OK = true;
    }