```
;;; (cl:merge! a b less?)
;;; takes two sorted lists a and b and smashes their cdr fields to form a
;;; single sorted list including the elements of both.
;;; Note: this does _not_ accept arrays.
;@
(define (cl:merge! a b less?)
(define (loop r a b)
(if (less? (car b) (car a))
(begin (set-cdr! r b)
(if (null? (cdr b))
(set-cdr! b a)
(loop b a (cdr b))))
;; (car a) <= (car b)
(begin (set-cdr! r a)
(if (null? (cdr a))
(set-cdr! a b)
(loop a (cdr a) b)))))
(cond ((null? a) b)
((null? b) a)
((less? (car b) (car a))
(if (null? (cdr b))
(set-cdr! b a)
(loop b a (cdr b)))
b)
(else (if (null? (cdr a))
(set-cdr! a b)
(loop a (cdr a) b))
a)))
```

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