public StringBuilder PrintBook(BookAndCount it_book)
{
StringBuilder str = new StringBuilder();
str.Append(it_book.book.ShowInfo());
str.Append(string.Format("\n" + "Количество экземпляров: " + it_book.count));
return(str);
}
public bool ContainsBook(BookAndCount b)
{
return(listBook.Contains(b));
}