(select
 (bgp
   (triple ?::?58 |http://www.w3.org/1999/02/22-rdf-syntax-ns#|:first ?:z)
   (triple ?::?58 |http://www.w3.org/1999/02/22-rdf-syntax-ns#|:rest
           |http://www.w3.org/1999/02/22-rdf-syntax-ns#|:nil))
 (?:z))