*/
  public static <T extends @Nullable Object> Iterable<T> concat(
      Iterable<? extends T> a, Iterable<? extends T> b) {
    return FluentIterable.concat(a, b);
  }

  /**
   * Combines three iterables into a single iterable. The returned iterable has an iterator that
   * traverses the elements in {@code a}, followed by the elements in {@code b}, followed by the

   * static final ImmutableSortedMap<Integer, String> INT_TO_WORD =
   *     new ImmutableSortedMap.Builder<Integer, String>(Ordering.natural())
   *         .put(1, "one")
   *         .put(2, "two")
   *         .put(3, "three")
   *         .buildOrThrow();
   * }</pre>
   *
   * <p>For <i>small</i> immutable sorted maps, the {@code ImmutableSortedMap.of()} methods are even
   * more convenient.
   *

   *
   * <pre>{@code
   * static final ImmutableMap<String, Integer> WORD_TO_INT =
   *     new ImmutableMap.Builder<String, Integer>()
   *         .put("one", 1)
   *         .put("two", 2)
   *         .put("three", 3)
   *         .buildOrThrow();
   * }</pre>
   *
   * <p>For <i>small</i> immutable maps, the {@code ImmutableMap.of()} methods are even more
   * convenient.
   *

   *
   * <pre>{@code
   * static final ImmutableBiMap<String, Integer> WORD_TO_INT =
   *     new ImmutableBiMap.Builder<String, Integer>()
   *         .put("one", 1)
   *         .put("two", 2)
   *         .put("three", 3)
   *         .buildOrThrow();
   * }</pre>
   *
   * <p>For <i>small</i> immutable bimaps, the {@code ImmutableBiMap.of()} methods are even more
   * convenient.
   *

 * of {@code Comparator} for pre-Java-8 users, in the same sense that {@link FluentIterable} is an
 * enriched {@link Iterable} for pre-Java-8 users.
 *
 * <h3>Three types of methods</h3>
 *
 * Like other fluent types, there are three types of methods present: methods for <i>acquiring</i>,
 * <i>chaining</i>, and <i>using</i>.
 *
 * <h4>Acquiring</h4>
 *
 * <p>The common ways to get an instance of {@code Ordering} are:

    Iterator<String> iterator = asList("one", "two", "three", "four", "five").iterator();
    try {
      Iterators.getOnlyElement(iterator);
      fail();
    } catch (IllegalArgumentException expected) {
      assertThat(expected)
          .hasMessageThat()
          .isEqualTo("expected one element but was: <one, two, three, four, five>");
    }
  }

        ImmutableMap.of("one", 1, "two", 2, "three", 3), "one", 1, "two", 2, "three", 3);
    assertMapEquals(
        ImmutableMap.of("one", 1, "two", 2, "three", 3, "four", 4),
        "one",
        1,
        "two",
        2,
        "three",
        3,
        "four",
        4);
    assertMapEquals(
        ImmutableMap.of("one", 1, "two", 2, "three", 3, "four", 4, "five", 5),
        "one",

      Iterator<? extends T> a, Iterator<? extends T> b) {
    checkNotNull(a);
    checkNotNull(b);
    return concat(consumingForArray(a, b));
  }

  /**
   * Combines three iterators into a single iterator. The returned iterator iterates across the
   * elements in {@code a}, followed by the elements in {@code b}, followed by the elements in