std::set<EdgeSpec> a_edges;  // actual edges
    // Get edges from inputs to body nodes and between body nodes
    for (const NodeDef& node_def : fdef.node_def()) {
      for (int i = 0; i < node_def.input_size(); ++i) {
        const string& in = node_def.input(i);
        const auto& v =
            a_edges.insert({in, absl::StrCat(node_def.name(), ":", i)});
        ASSERT_TRUE(v.second) << "Duplicate edge " << in << " -> "