core.clj

  (let [data [[:a :x 1]
              [:b :x 2]
              [:c :y 3]]
        subquery (<- [?set ?num1]
                     (data ?label ?set ?num)
                     (:sort ?num)
                     (:reverse true)
                     (c/limit [1] :< ?num :> ?num1))]
    (?<- (stdout)
         [?label ?set ?num]
         (data ?label ?set _)
         (subquery ?set ?num)))