May I suggest the following addition to the SRFI-1 list library, Common Lisp's
LDIFF:

I think a reasonable definition is:

(define (ldiff l subl)
  (cond
   ((null? l) '())
   ((eq? (cdr l) subl) (list (car l)))
   (else (cons (car l)
	       (ldiff (cdr l) subl)))))

(I sent this as private email before, but am now sending it to the mailing list)