  Exercise 3.16
;
;
  Show that    procedure to count pairs is flawed .
;
;(define (count-pairs x)
;  (if (not (pair? x))
;      0
;      (+ (count-pairs (car x))
          ( count - pairs    ) )
          1 ) ) )
;
  Give example of 3 pair box - and - pointers that return 3 , 4 , 7 , and
; never return.
;
;
; Returns 3
;
; z-->* * * * *  * * * * *  * * * * *
;     * a *   *->* b *   *->* c * / *
;     * * * * *  * * * * *  * * * * *
;
; Returns 4
;
; z-->* * * * *  * * * * *  * * * * *
;     * a *   *->*   *   *->* c * / *
;     * * * * *  * | * * *  * * * * *
;                  |          ^
;                  -----------|
; Returns 7
;
; z-->* * * * *  * * * * *  * * * * *
;     *   *   *->*   *   *->* c * / *
;     * | * * *  * * * * *  * * * * *
;       |         ^ \         ^
;       ---------/   --------/
;
; Never return
;
; z-->* * * * *  * * * * *  * * * * *
;     * a *   *->* b *   *->* c *   *
;     * * * * *  * * * * *  * * * * *
;       ^                         |
;       |--------------------------




(define (count-pairs x)
  (if (not (pair? x))
      0
      (+ (count-pairs (car x))

 never return.


 Returns 3

 z-->* * * * *  * * * * *  * * * * *
     * a *   *->* b *   *->* c * / *
     * * * * *  * * * * *  * * * * *

 Returns 4

 z-->* * * * *  * * * * *  * * * * *
     * a *   *->*   *   *->* c * / *
     * * * * *  * | * * *  * * * * *
                  |          ^
                  -----------|
 Returns 7

 z-->* * * * *  * * * * *  * * * * *
     *   *   *->*   *   *->* c * / *
     * | * * *  * * * * *  * * * * *
       |         ^ \         ^
       ---------/   --------/

 Never return

 z-->* * * * *  * * * * *  * * * * *
     * a *   *->* b *   *->* c *   *
     * * * * *  * * * * *  * * * * *
       ^                         |
       |--------------------------
  Exercise 3.16
  Show that    procedure to count pairs is flawed .
          ( count - pairs    ) )
          1 ) ) )
  Give example of 3 pair box - and - pointers that return 3 , 4 , 7 , and
