public static String toBibTex(Reference ref) {
        if (ref.getClass().isAssignableFrom(Book.class)) {
            return bookToBibTex((Book) ref);
        } else if (ref.getClass().isAssignableFrom(Article.class)) {
            return articleToBibTex((Article) ref);
        } else if (ref.getClass().isAssignableFrom(Inproceeding.class)) {
            return inproceedingToBibTex((Inproceeding) ref);
        }
        return null;