public ActionResult CreateAuthor(int id)
        {
            Book   foundBook = Book.Find(id);
            Author newAuthor = new Author(Request.Form["author-first"], Request.Form["author-last"]);

            Author.CheckDuplicate(newAuthor);
            foundBook.AddAuthor(newAuthor);

            return(RedirectToAction("Details", new { Id = id }));
        }