/**
 * A non-public interface for the methods shared between {@link Graph}, {@link ValueGraph}, and
 * {@link Network}.
 *
 * @author Joshua O'Madadhain
 * @param <N> Node parameter type
 */
interface ArchetypeGraph<N> extends SuccessorsFunction<N>, PredecessorsFunction<N> {
  //
  // Graph-level accessors
  //

  /** Returns all nodes in this graph, in the order specified by {@link #nodeOrder()}. */
  Set<N> nodes();

abstract class IncidentEdgeSet<N> extends AbstractSet<EndpointPair<N>> {
  final N node;
  final ArchetypeGraph<N> graph;
  final EdgeType edgeType;

  enum EdgeType {
    INCOMING, // incoming incident edges only
    OUTGOING, // outgoing incident edges only
    BOTH // both incoming and outgoing incident edges
  }

  IncidentEdgeSet(ArchetypeGraph<N> graph, N node, EdgeType edgeType) {
    this.graph = graph;
    this.node = node;

abstract class IncidentEdgeSet<N> extends AbstractSet<EndpointPair<N>> {
  final N node;
  final ArchetypeGraph<N> graph;
  final EdgeType edgeType;

  enum EdgeType {
    INCOMING, // incoming incident edges only
    OUTGOING, // outgoing incident edges only
    BOTH // both incoming and outgoing incident edges
  }

  IncidentEdgeSet(ArchetypeGraph<N> graph, N node, EdgeType edgeType) {
    this.graph = graph;
    this.node = node;