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

      this.children = asList(children);
    }
  }

  private static final TreeTraverser<Tree> ADAPTER =
      new TreeTraverser<Tree>() {
        @Override
        public Iterable<Tree> children(Tree node) {
          return node.children;
        }
      };

  private static final TreeTraverser<Tree> ADAPTER_USING_USING =
      TreeTraverser.using(
          new Function<Tree, Iterable<Tree>>() {
            @Override