(define (make-eq-map)
  (define alist '())
  (define interned-alist '())
  (define counter 0)
  (lambda (msg obj)
    (case msg
      ((contains?) (assq obj alist))
      ((cycle-counter)
       (set! interned-alist (cons obj interned-alist))
       (let ((num (cdr (assq obj alist))))
         (string->symbol (string-append
                          "#"
                          (number->string num)
                          "#"))))
      ((cycle-used?) (memq obj interned-alist))
      ((intern!)
       (set! alist (cons (cons obj counter) alist))
       (set! counter (+ counter 1)))
      (else (error 'make-eq-map
                   "invalid message"
                   msg)))))