private void lbBooks_SelectedIndexChanged(object sender, EventArgs e)
{
lbAvailableCopies.Items.Clear();
lbCopies.Items.Clear();
Book selectedBook = lbBooks.SelectedItem as Book;
IEnumerable <Loan> allLoans = loanService.AllBookCopiesOnLoan();
IEnumerable <BookCopy> bookCopies = bookCopyService.AllExceptWithBook(allLoans, selectedBook);
ShowAllAvailableCopies(bookCopies);
ShowAllBookCopiesForBook(bookCopyService.AllCopiesForBook(selectedBook));
}