*
   * {@snippet :
   * b ---- a ---- d
   * |      |
   * |      |
   * e ---- c ---- f
   * }
   */
  private static final SuccessorsFunction<Character> JAVADOC_GRAPH =
      createUndirectedGraph("ba", "ad", "be", "ac", "ec", "cf");

  /**
   * A diamond shaped directed graph (arrows going down):
   *
   * {@snippet :
   *   a
   *  / \
   * b   c
   *  \ /

   * respective source streams. For example:
   *
   * {@snippet :
   * Streams.forEachPair(
   *   Stream.of("foo1", "foo2", "foo3"),
   *   Stream.of("bar1", "bar2"),
   *   (arg1, arg2) -> System.out.println(arg1 + ":" + arg2)
   * }
   *
   * <p>will print:
   *
   * {@snippet :
   * foo1:bar1
   * foo2:bar2
   * }
   *

 * reasonably accurate values are sufficient. If the uncommon case that you need to maximize
 * accuracy, use {@code System.nanoTime()} directly instead.
 *
 * <p>Basic usage:
 *
 * {@snippet :
 * Stopwatch stopwatch = Stopwatch.createStarted();
 * doSomething();
 * stopwatch.stop(); // optional
 *
 * Duration duration = stopwatch.elapsed();
 *

 * annotated by {@link TestSubtype}.
 *
 * <p>These declaration methods rely on Java static type checking to make sure what we want to
 * assert as subtypes are really subtypes according to javac. For example:
 *
 * {@snippet :
 * class MySubtypeTests extends SubtypeTester {
 *   @TestSubtype(suppressGetSubtype = true, suppressGetSupertype = true)
 *   public <T> Iterable<? extends T> listIsSubtypeOfIterable(List<T> list) {

 * href="http://tools.ietf.org/html/rfc4648">RFC 4648</a>. For example, the expression:
 *
 * {@snippet :
 * BaseEncoding.base32().encode("foo".getBytes(US_ASCII))
 * }
 *
 * <p>returns the string {@code "MZXW6==="}, and
 *
 * {@snippet :
 * byte[] decoded = BaseEncoding.base32().decode("MZXW6===");
 * }
 *
 * <p>...returns the ASCII bytes of the string {@code "foo"}.
 *

   * Maps#asMap(Set, Function)}.
   *
   * <p><b>Note:</b> on Java 8+, it is usually better to use streams. For example:
   *
   * {@snippet :
   * import static com.google.common.collect.ImmutableMap.toImmutableMap;
   * ...
   * ImmutableMap<Color, String> colorNames =
   *     allColors.stream().collect(toImmutableMap(c -> c, c -> c.toString()));

   * through the returned queue.
   *
   * <p>It is imperative that the user manually synchronize on the returned queue when accessing the
   * queue's iterator:
   *
   * {@snippet :
   * Queue<E> queue = Queues.synchronizedQueue(MinMaxPriorityQueue.<E>create());
   * ...
   * queue.add(element);  // Needn't be in synchronized block
   * ...

 * annotated by {@link TestSubtype}.
 *
 * <p>These declaration methods rely on Java static type checking to make sure what we want to
 * assert as subtypes are really subtypes according to javac. For example:
 *
 * {@snippet :
 * class MySubtypeTests extends SubtypeTester {
 *   @TestSubtype(suppressGetSubtype = true, suppressGetSupertype = true)
 *   public <T> Iterable<? extends T> listIsSubtypeOfIterable(List<T> list) {

   * through the returned queue.
   *
   * <p>It is imperative that the user manually synchronize on the returned queue when accessing the
   * queue's iterator:
   *
   * {@snippet :
   * Queue<E> queue = Queues.synchronizedQueue(MinMaxPriorityQueue.<E>create());
   * ...
   * queue.add(element);  // Needn't be in synchronized block
   * ...

 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To
 * create an instance of one of the built-in implementations of {@code Network}, use the {@link
 * NetworkBuilder} class:
 *
 * {@snippet :
 * MutableNetwork<Integer, MyEdge> network = NetworkBuilder.directed().build();
 * }
 *
 * <p>{@link NetworkBuilder#build()} returns an instance of {@link MutableNetwork}, which is a