(prefix ((ex: <http://www.example.org/schema#>)
         (in: <http://www.example.org/instance#>))
  (project (?x ?max)
    (join #sequence
      (project (?max)
        (assign ((?max ?/.0))
          (group () ((?/.0 (max ?/y)))
            (bgp (triple ?/x ex:p ?/y)))))
      (bgp (triple ?x ex:p ?max)))))