public static bool AddBook(Book book) { if (!books.ContainsKey(book.Isbn)) { books.Add(book.Isbn, book); amounts[book.Isbn] = 1; Serializer.AddBook(book.GetModel()); return(true); } else { amounts[book.Isbn]++; Serializer.IncreaseAmount(book.Isbn, 1); return(false); } }