(define find
  (lambda (target lst)
    (cond
      ((null? lst)
       lst)
      ((= target (car lst))
       lst)
      (else
       (find target (cdr lst))))))

(define member?
  (lambda (target lst)
    (not (null? (find target lst)))))

(define two-members?
  (lambda (target1 target2 lst)
    (member? target2 (find target1 lst))))

(define three-members?
  (lambda (target1 target2 target3 lst)
    (two-members? target2 target3 (find target1 lst))))

(define n-members?
  (lambda (n target lst)
    (cond
      ((zero? n) #t)
      (else (let ((lst (find target lst)))
              (cond
                ((null? lst) #f)
                (else (n-members? (- n 1) target (cdr lst)))))))))