Проследить вызовы функции

(defun fact (n) 
  (if (zerop n)
      1   
      (* n (fact (- n 1)))))
(trace fact)
(fact 3)
(untrace fact)

0: (FACT 3)
  1: (FACT 2)
    2: (FACT 1)
      3: (FACT 0)
      3: FACT returned 1
    2: FACT returned 1
  1: FACT returned 2
0: FACT returned 6
6