* a {@link Graph}.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 */
interface GraphConnections<N, V> {

  Set<N> adjacentNodes();

  Set<N> predecessors();

  Set<N> successors();

  /**
   * Returns an iterator over the incident edges.
   *

import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * An implementation of {@link GraphConnections} for undirected graphs.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 */
final class UndirectedGraphConnections<N, V> implements GraphConnections<N, V> {
  private final Map<N, V> adjacentNodeValues;

  }

  private static <N, V> ImmutableMap<N, GraphConnections<N, V>> getNodeConnections(
      ValueGraph<N, V> graph) {
    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
    // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
    // input nodes are sorted.
    ImmutableMap.Builder<N, GraphConnections<N, V>> nodeConnections = ImmutableMap.builder();

import org.jspecify.annotations.Nullable;

/**
 * An implementation of {@link GraphConnections} for directed graphs.
 *
 * @author James Sexton
 * @author Jens Nyman
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 */
final class DirectedGraphConnections<N, V> implements GraphConnections<N, V> {
  /**
   * A wrapper class to indicate a node is both a predecessor and successor while still providing