(select
 (bgp
   (triple <http://example.org/ns#x> ?:p ?::?16)
   (triple ?::?16 |http://www.w3.org/1999/02/22-rdf-syntax-ns#|:first 1)
   (triple ?::?16 |http://www.w3.org/1999/02/22-rdf-syntax-ns#|:rest
           |http://www.w3.org/1999/02/22-rdf-syntax-ns#|:nil))
 (?:p))