(define (make-queue)
	  (let ((front-ptr '())
	        (rear-ptr '()))

	    (define (insert-queue! item)
	      (let ((new-pair (cons item '())))
	        (cond ((null? front-ptr)
	               (set! front-ptr new-pair)
	               (set! rear-ptr new-pair))
	              (else
	               (set-cdr! rear-ptr new-pair)
	               (set! rear-ptr new-pair)))))

	    (define (delete-queue!)
	      (cond ((null? front-ptr)
	             (error "DELETE! called with an empty queue"))
	            (else
	             (set! front-ptr (cdr front-ptr)))))

	    (define (print-queue)
	      (display front-ptr))

	    (define (dispatch m)
	      (cond ((eq? m 'insert) insert-queue!)
	            ((eq? m 'delete) (delete-queue!))
	            ((eq? m 'print) (print-queue))
	            (else
	             (error "Error operator"))))
	    dispatch))

	(define q1 (make-queue))

	((q1 'insert) 'a)
	(q1 'print)
	((q1 'insert) 'b)
	(q1 'print)
	(q1 'delete)
	(q1 'print)
	(q1 'delete)
	(q1 'print)