#for $author in $sorted($books_by_author)
#set $books = $books_by_author[$author]
#for $book in $books
#if $book.series != $series
#set $series = $book.series
<tr>
#for $author in $sorted($books_by_author)
#set $books = $books_by_author[$author]
#for $book in $books
#if $book.series != $series
#set $series = $book.series
<tr>