*       behavior is undefined
   * </ul>
   *
   * @throws IllegalArgumentException if {@code edge} is not an element of this network
   */
  Set<E> adjacentEdges(E edge);

  /**
   * Returns a live view of the set of edges that each directly connect {@code nodeU} to {@code
   * nodeV}.
   *

   *       behavior is undefined
   * </ul>
   *
   * @throws IllegalArgumentException if {@code edge} is not an element of this network
   */
  Set<E> adjacentEdges(E edge);

  /**
   * Returns a live view of the set of edges that each directly connect {@code nodeU} to {@code
   * nodeV}.
   *