(def power (nbr power)
      (if (is power 0)
          1
          (if (> power 0)
	      (let acc nbr
    		  (for x 1 (- power 1)
        	  	(= acc (* acc nbr))) acc)
	      (let acc 1
    		  (for x 0 power -1
			(= acc (/ acc nbr))) acc))))