> (trace fact) (fact) > (fact 5) 0: (fact 5) 1: (fact 4) 2: (fact 3) 3: (fact 2) 4: (fact 1) 5: (fact 0) 5: returned 1 4: returned 1 3: returned 2 2: returned 6 1: returned 24 0: returned 120 120