; recursive
(
  (clear) 
  (defn rec 
    (v) 
    (if 
      (gt v 0) 
      (
        (stroke 
          (circle 
            (mul 5 v) 
            (mul 5 v) 
            (mul 5 v)) 1 "red") 
        (rec 
          (sub v 5))))) 
  (rec 100))