(define gv (show-graph (digraph '(1 2 3) '((1 1) (3 3)))))
(define (symmetric gv)
      (not (member #f 
                 (map (lambda (x)
                         (set! (color x) "green")
                         (let ((e (is-edge (ref (vertices x) 1) 
                                           (ref (vertex x) 0))) 
                                 (cond (e  (jiggle (edge-item e)) #t)
                                       (#t (set! (color x) "red") #f))))
                      (edges gv)))))
(symmetric gv)
