public static string GetSeriesReport(List<Book> books)
        {
            IDocumentFormatDefinition<BookAggregatedGroup<int>> definition = StatReportDefinition<int>.GenericBookGroupReportFormat();

            return definition.Export(books
                .DenormaliseAuthors()
                .RemoveBooksWithoutSeries()
                .GroupBySeries());
        }
        public static string GetAuthorCountReport(List<Book> books)
        {
            IDocumentFormatDefinition<BookAggregatedGroup<int>> definition = StatReportDefinition<int>.GenericBookGroupReportFormat();

            return definition.Export(books.DenormaliseAuthors().GroupByAuthorBookCount());
        }