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

declare function fun:closure($input as node()*, $result as node()*) as node()*
{
   let $current := $input/parlist/listitem/parlist/listitem
   let $new := $current except $result 
   let $all := ($result,$new) 
 
   return
      if(exists($new)) 
      then ($new, fun:closure($new,$all))
      else ()
};

doc()//listitem[text/keyword or fun:closure(.,())/text/keyword]/text/keyword