}
      }
    }
  }
  for (const BackEdge& be : back_edges_) {
    graph_->RemoveEdge(be.edge);
  }
  return absl::OkStatus();
}

const std::vector<BackEdgeHelper::BackEdge>& BackEdgeHelper::RemovedEdges()
    const {
  return back_edges_;
}

Status BackEdgeHelper::Replace() {
  if (graph_ == nullptr) {
    return errors::Internal("BackEdgeHelper Replace called before Remove.");
  }
  if (replaced_) {