* implement it:
 *
 * {@snippet :
 * // won't work
 * TreeTraverser<NodeType> traverser = node -> node.getChildNodes();
 * }
 *
 * Instead, you can pass a lambda expression to the {@code using} factory method:
 *
 * {@snippet :
 * TreeTraverser<NodeType> traverser = TreeTraverser.using(node -> node.getChildNodes());
 * }
 *
 * @author Louis Wasserman
 * @since 15.0

 * implement it:
 *
 * {@snippet :
 * // won't work
 * TreeTraverser<NodeType> traverser = node -> node.getChildNodes();
 * }
 *
 * Instead, you can pass a lambda expression to the {@code using} factory method:
 *
 * {@snippet :
 * TreeTraverser<NodeType> traverser = TreeTraverser.using(node -> node.getChildNodes());
 * }
 *
 * @author Louis Wasserman
 * @since 15.0

      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {
        return viewer.preOrderTraversal(root);
      }
    },
    POST_ORDER {
      @Override
      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {
        return viewer.postOrderTraversal(root);
      }
    },
    BREADTH_FIRST {
      @Override
      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {

      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {
        return viewer.preOrderTraversal(root);
      }
    },
    POST_ORDER {
      @Override
      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {
        return viewer.postOrderTraversal(root);
      }
    },
    BREADTH_FIRST {
      @Override
      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {

FIELD com.google.common.collect.Sets.SubSet.inputSet
FIELD com.google.common.collect.SingletonImmutableBiMap.inverse
FIELD com.google.common.collect.TreeTraverser.PostOrderNode.childIterator
FIELD com.google.common.collect.TreeTraverser.PreOrderIterator.stack
FIELD com.google.common.util.concurrent.AbstractFuture.Listener.executor com.google.common.util.concurrent.MoreExecutors.rejectionPropagatingExecutor.$