/guava/guava/src/com/google/common/graph/Traverser.java
Iterator<? extends N> top = horizon.removeFirst( ) ;
Iterator<? extends N> top = horizon.getFirst ( ) ;
} static <N> Traversal<N> inTree(SuccessorsFunction<N> tree) { return new Traversal<N>(tree) { @CheckForNull @Override N visitNext(Deque<Iterator<? extends N>> horizon) { <extra_id_0> if (top.hasNext()) { return checkNotNull(top.next()); } horizon.removeFirst(); return null; }