#| BEGIN (Write your solution here) |#
(define (squarer a b)
  (define (process-new-value)
    (if (has-value? b)
        (if (< (get-value b) 0)
            (error "square less than 0 -- SQUARER" (get-value b))
            (set-value! a (sqrt (get-value b)) me))
        (when (has-value? a)
          (set-value! b (* (get-value a) (get-value a)) me))))
    (define (process-forget-value)
      (forget-value! a me)
      (forget-value! b me)
      (process-new-value))
    (define (me request)
      (cond ((eq? request 'I-have-a-value)
             (process-new-value))
            ((eq? request 'I-lost-my-value)
             (process-forget-value))
            (else
             (error "Unknown request -- SQUARER" request))))
    (connect a me)
    (connect b me)
    me)
#| END |#