$ clisp

<...snip...>

[1]> (load "reduce-to-set.l")
;; Loading file reduce-to-set.l ...
;; Loaded file reduce-to-set.l
T
[2]> :(trace reduce-to-set)
:||
[3]>
;; Tracing function REDUCE-TO-SET.
(REDUCE-TO-SET)
[4]> (reduce-to-set '())
1. Trace: (REDUCE-TO-SET 'NIL)
1. Trace: REDUCE-TO-SET ==> NIL
NIL
[5]> (reduce-to-set '(1 2))
1. Trace: (REDUCE-TO-SET '(1 2))
2. Trace: (REDUCE-TO-SET '(2))
3. Trace: (REDUCE-TO-SET 'NIL)
3. Trace: REDUCE-TO-SET ==> NIL
2. Trace: REDUCE-TO-SET ==> (2)
1. Trace: REDUCE-TO-SET ==> (1 2)
(1 2)
[6]> (reduce-to-set '(1 2 3 2 1))
1. Trace: (REDUCE-TO-SET '(1 2 3 2 1))
2. Trace: (REDUCE-TO-SET '(2 3 2 1))
3. Trace: (REDUCE-TO-SET '(3 2 1))
4. Trace: (REDUCE-TO-SET '(2 1))
5. Trace: (REDUCE-TO-SET '(1))
6. Trace: (REDUCE-TO-SET 'NIL)
6. Trace: REDUCE-TO-SET ==> NIL
5. Trace: REDUCE-TO-SET ==> (1)
4. Trace: REDUCE-TO-SET ==> (2 1)
3. Trace: REDUCE-TO-SET ==> (3 2 1)
2. Trace: REDUCE-TO-SET ==> (3 2 1)
1. Trace: REDUCE-TO-SET ==> (3 2 1)
(3 2 1)
[7]> (reduce-to-set '(a a b a b c a b c d))
1. Trace: (REDUCE-TO-SET '(A A B A B C A B C D))
2. Trace: (REDUCE-TO-SET '(A B A B C A B C D))
3. Trace: (REDUCE-TO-SET '(B A B C A B C D))
4. Trace: (REDUCE-TO-SET '(A B C A B C D))
5. Trace: (REDUCE-TO-SET '(B C A B C D))
6. Trace: (REDUCE-TO-SET '(C A B C D))
7. Trace: (REDUCE-TO-SET '(A B C D))
8. Trace: (REDUCE-TO-SET '(B C D))
9. Trace: (REDUCE-TO-SET '(C D))
10. Trace: (REDUCE-TO-SET '(D))
11. Trace: (REDUCE-TO-SET 'NIL)
11. Trace: REDUCE-TO-SET ==> NIL
10. Trace: REDUCE-TO-SET ==> (D)
9. Trace: REDUCE-TO-SET ==> (C D)
8. Trace: REDUCE-TO-SET ==> (B C D)
7. Trace: REDUCE-TO-SET ==> (A B C D)
6. Trace: REDUCE-TO-SET ==> (A B C D)
5. Trace: REDUCE-TO-SET ==> (A B C D)
4. Trace: REDUCE-TO-SET ==> (A B C D)
3. Trace: REDUCE-TO-SET ==> (A B C D)
2. Trace: REDUCE-TO-SET ==> (A B C D)
1. Trace: REDUCE-TO-SET ==> (A B C D)
(A B C D)
[8]> (bye)
Bye.