(defmacro pruning-sudoku [board out]
  (let [lvars (repeatedly 81 gensym)
        [vrows vcols vblocks] (slice lvars)
        [rows cols blocks] (slice (reduceable-board board))]
    (concat
      `(exist [~@lvars]
              (== ~out (list ~@lvars)))
      (interleave
        (map (fn [vrow row]
               `(prune-o (list ~@row) (list ~@vrow)))
             vrows rows)
        (map (fn [vcol col]
               `(prune-o (list ~@col) (list ~@vcol)))
             vcols cols)
        (map (fn [vblock block]
               `(prune-o (list ~@block) (list ~@vblock)))
             vblocks blocks)))))