// v1-->v2
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.2", true, null, null, 2, 2));

        // v1-->v3
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.2", true, null, null, 4, 2));

        // v3-->v4

        // v1-->v2
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.2", true, null, null, 2, 2));

        // v1-->v3
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.2", true, null, null, 4, 2));

        // v3-->v4

                    // gathered with problem collector
                }
                return null;
            }
        };
    }

    private boolean addEdge(Path from, Path p, DefaultModelProblemCollector problems) {
        try {
            dag.addEdge(from.toString(), p.toString());
            return true;
        } catch (Graph.CycleDetectedException e) {
            problems.add(new DefaultModelProblem(

	if _, ok := g.byLabel[label]; ok {
		return false
	}
	g.byLabel[label] = len(g.Nodes)
	g.Nodes = append(g.Nodes, label)
	g.edges[label] = map[string]bool{}
	return true
}

func (g *Graph) AddEdge(from, to string) {
	g.edges[from][to] = true
}

func (g *Graph) DelEdge(from, to string) {
	delete(g.edges[from], to)
}

func (g *Graph) HasEdge(from, to string) bool {

import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

class Graph {

    final Map<String, Set<String>> graph = new LinkedHashMap<>();

    synchronized void addEdge(String from, String to) throws CycleDetectedException {
        if (graph.computeIfAbsent(from, l -> new HashSet<>()).add(to)) {

    auto sink = ops::Identity(scope.WithOpName("sink"), exit);

    // Remove the dummy node and add the loop backedge.
    scope.graph()->RemoveNode(dummy.node());
    scope.graph()->AddEdge(next_iteration.node(), 0, merge.output.node(), 1);

    TF_EXPECT_OK(scope.ToGraph(&graph));
  }

  GraphShapeInfo shape_info;
  TF_ASSERT_OK(InferShapes(&graph, /*arg_shapes=*/{}, /*fnlib_def=*/nullptr,

      << "Use of BlockArgument encounted before def!";
  // For argument, there is only one result output, so the index is always 0.
  graph_->AddEdge(input_node_it->second, 0, dst_node, dst_index);
  return absl::OkStatus();
}

Status Exporter::AddEdge(Operation* inst) {
  // For tf_executor.fetch, add only its data edges. Control edges are captured
  // later.

      << "Use of BlockArgument encounted before def!";
  // For argument, there is only one result output, so the index is always 0.
  graph_->AddEdge(input_node_it->second, 0, dst_node, dst_index);
  return absl::OkStatus();
}

Status Exporter::AddEdge(Operation* inst) {
  // For tf_executor.fetch, add only its data edges. Control edges are captured
  // later.

    public Collection<Vertex> getVertices() {
        return vertices.values();
    }

    Vertex addVertex(String label) {
        return vertices.computeIfAbsent(label, Vertex::new);
    }

    void addEdge(Vertex from, Vertex to) throws CycleDetectedException {
        from.children.add(to);
        to.parents.add(from);
        List<String> cycle = findCycle(to);
        if (cycle != null) {

              graph->RemoveEdge(e);
            } else {
              Node* dst = e->dst();
              int dst_input = e->dst_input();
              graph->RemoveEdge(e);
              graph->AddEdge(const_node, 0, dst, dst_input);
            }
          }
        }
      }
    }

    // Merge node causes a loop so we remove NextIteration->Merge edge before