public void AddBookstoLibrary(Book book)
 {
     Library.booksList.Add(book);
 }
 public void ReturnBook(Book book)
 {
     this.rentedBooks.Remove(book);
 }
 public void Rent(Book book)
 {
     RentBook(book);
 }
 public void RentBook(Book book)
 {
     this.rentedBooks.Add(book);
 }
 public void Rented(Book book)
 {
     this.Rentee = "Rentee";
 }