gistfile1.txt

(remove-child!
  (lambda (parent child)
    (if (enum-set-contains? 
          (apply enum-set-union
              (map (curry vertex-parents graph)
                (vertex-children graph child)))
          parent)
      (void)
      (begin 
        (enum-set-remove! (vector-ref mb parent) child)
        (enum-set-remove! (vector-ref mb child) parent)))
    (for-enum-set ([other-parent (vertex-parents graph child)])
      (unless (equal? parent other-parent)
        (define others-child (vertex-children graph other-parent))
        (define others-parent (vertex-parents graph other-parent))
        (define others-childs-parents ((apply enum-set-union
                                        (map (curry vertex-parents graph)
                                          (vertex-children graph other-parent)))))
        (if (enum-set-contains? (enum-set-union others-parent others-child
            others-childs-parents) parent)
          (void)
          (begin 
            (enum-set-remove! (vector-ref mb parent) other-parent)
              (enum-set-remove! (vector-ref mb other-parent) parent)))))))