{ for $book1 in doc("bib.xml")//book, $book2 in doc("bib.xml")//book let $aut1 := for $a in $book1/author order by $a/last, $a/first return $a let $aut2 := for $a in $book2/author order by $a/last, $a/first return $a where $book1 << $book2 and not($book1/title = $book2/title) and deep-equal($aut1, $aut2) return { $book1/title } { $book2/title } }