declare namespace fun = 'have.more.fun';

declare function fun:closure($input as node()*, $result as node()*) as node()*
{
   let $current := $input/seller/id(@person)/watches/watch/id(@open_auction)
   let $new := $current except $result 
   let $all := ($result,$new) 
 
   return
      if(exists($new)) 
      then ($new, fun:closure($new,$all))
      else ()
};

doc()/site/open_auctions/open_auction[position() <= 5]/fun:closure(.,())/interval