(define (graph-match G1 G2)
  (let ([matchings (make-set)])
   (let match-loop ([s (make-set)])
    (cond
      [(set= (set-map cdr s)
             (graph-vertices G2))
       (set-add! s matchings)]
      [else (for-each (lambda (vertex-pair)
                        (let ([n (car vertex-pair)]
                              [m (cdr vertex-pair)])
                          (when (and (syntactic-feasibility? s n m)
                                     (semantic-feasibility? s n m))
                            (match-loop (set-union s (cons n m))))))
                      (candidate-pairs s G1 G2))]))
   (set->list matchings)))