-*- Mode:Text; Package:USER -*-
(defun tak (x y z)
  (if (not (< y x))
      z
    (tak (tak (1- x) y z)
	 (tak (1- y) z x)
	 (tak (1- z) x y))))

TAK:
 16 PUSH ARG|1                ;Y
 17 < ARG|0                   ;X
 18 BR-NOT-NIL 20
 19 MOVE D-RETURN ARG|2       ;Z
 20 CALL D-RETURN FEF|6       ;#'TAK
 21 CALL D-PDL FEF|6          ;#'TAK
 22 PUSH 1- ARG|0             ;X
 23 PUSH ARG|1                ;Y
 24 MOVE D-LAST ARG|2         ;Z
 25 CALL D-PDL FEF|6          ;#'TAK
 26 PUSH 1- ARG|1             ;Y
 27 PUSH ARG|2                ;Z
 28 MOVE D-LAST ARG|0         ;X
 29 CALL D-LAST FEF|6         ;#'TAK
 30 PUSH 1- ARG|2             ;Z
 31 PUSH ARG|0                ;X
 32 MOVE D-LAST ARG|1         ;Y


(tak 18. 12. 6)

(1 ENTER TAK: 18 12 6)
  (2 ENTER TAK: 17 12 6)
    (3 ENTER TAK: 16 12 6)
      (4 ENTER TAK: 15 12 6)
        (5 ENTER TAK: 14 12 6)
          (6 ENTER TAK: 13 12 6)
            (7 ENTER TAK: 12 12 6)
            (7 EXIT TAK: 6)
            (7 ENTER TAK: 11 6 13)
              (8 ENTER TAK: 10 6 13)
                (9 ENTER TAK: 9 6 13)
                  (10 ENTER TAK: 8 6 13)
                    (11 ENTER TAK: 7 6 13)
                      (12 ENTER TAK: 6 6 13)
                      (12 EXIT TAK: 13)
                      (12 ENTER TAK: 5 13 7)
                      (12 EXIT TAK: 7)
                      (12 ENTER TAK: 12 7 6)
                        (13 ENTER TAK: 11 7 6)
                          (14 ENTER TAK: 10 7 6)
                            (15 ENTER TAK: 9 7 6)
                              (16 ENTER TAK: 8 7 6)
                                (17 ENTER TAK: 7 7 6)
                                (17 EXIT TAK: 6)
                                (17 ENTER TAK: 6 6 8)
                                (17 EXIT TAK: 8)
                                (17 ENTER TAK: 5 8 7)
                                (17 EXIT TAK: 7)
                                (17 ENTER TAK: 6 8 7)
                                (17 EXIT TAK: 7)
                              (16 EXIT TAK: 7)

We examine the first level 16 call to tak from its entry, through 3
function calls, and this its exit.

(tak 8. 7. 6.)
 16 PUSH ARG|1                ;Y <7>
 17 < ARG|0                   ;X <8>
 18 BR-NOT-NIL 20
 ...
 20 CALL D-RETURN FEF|6       ;#'TAK
 21 CALL D-PDL FEF|6          ;#'TAK
 22 PUSH 1- ARG|0             ;X <8>
 23 PUSH ARG|1                ;Y <7>
 24 MOVE D-LAST ARG|2         ;Z <6>
   (tak 7 7 6)
   16 PUSH ARG|1                ;Y <7>
   17 < ARG|0                   ;X <7>
   18 BR-NOT-NIL 20
   19 MOVE D-RETURN ARG|2       ;Z <6>
      ... return is to D-PDL ...
 25 CALL D-PDL FEF|6          ;#'TAK
 26 PUSH 1- ARG|1             ;Y <7>
 27 PUSH ARG|2                ;Z <6>
 28 MOVE D-LAST ARG|0         ;X <8>
   (tak 6 6 8)
   16 PUSH ARG|1                ;Y <6>
   17 < ARG|0                   ;X <6>
   18 BR-NOT-NIL 20
   19 MOVE D-RETURN ARG|2       ;Z <8>
      ... return is to D-PDL ...
 29 CALL D-LAST FEF|6         ;#'TAK
 30 PUSH 1- ARG|2             ;Z <6>
 31 PUSH ARG|0                ;X <8>
 32 MOVE D-LAST ARG|1         ;Y <7>
   (tak 5 8 7)
   16 PUSH ARG|1                ;Y <8>
   17 < ARG|0                   ;X <5>
   18 BR-NOT-NIL 20
   19 MOVE D-RETURN ARG|2       ;Z <7>
      ... return is to D-LAST ...
   (tak 6 8 7)   
   16 PUSH ARG|1                ;Y <8>
   17 < ARG|0                   ;X <6>
   18 BR-NOT-NIL 20
   19 MOVE D-RETURN ARG|2       ;Z <7>
      ... return is to D-RETURN ...