(de powers (M)
   (co (intern (pack 'powers M))
      (for (I 0 (inc 'I))
         (yield (** I M)) ) ) )

(de filtered (N M)
   (co 'filtered
      (let (V (powers N)  F (powers M))
         (loop
            (if (> V F)
               (setq F (powers M))
               (and (> F V) (yield V))
               (setq V (powers N)) ) ) ) ) )

(do 20 (filtered 2 3))
(do 10 (println (filtered 2 3)))