return new Iterator<U>() {
            @Override
            public boolean hasNext() {
                return it.hasNext();
            }

            @Override
            public U next() {
                return mapper.apply(it.next());
            }
        };
    }

    @Override
    public int size() {
        return list.size();
    }

    final Runnable runnable;
    final Executor executor;
    @CheckForNull RunnableExecutorPair next;

    RunnableExecutorPair(
        Runnable runnable, Executor executor, @CheckForNull RunnableExecutorPair next) {
      this.runnable = runnable;
      this.executor = executor;
      this.next = next;
    }
  }

      // unlink guard from activeGuards
      for (Guard p = activeGuards, pred = null; ; pred = p, p = p.next) {
        if (p == guard) {
          if (pred == null) {
            activeGuards = p.next;
          } else {
            pred.next = p.next;
          }
          p.next = null; // help GC
          break;
        }
      }
    }
  }

  /*

     * stack so that it is returned by the next call to {@link Iterator#next()}. If the element is
     * not in {@link #nextElements}, this method throws an {@link UnknownElementException}.
     *
     * <p>This method is used when testing iterators without a known ordering. We poll the target
     * iterator's next element and pass it to the reference iterator through this method so it can

    if (supportsRemove) {
      int initialSize = map.size();
      boolean didRemove = entrySet.remove(entrySet.iterator().next());
      assertTrue(didRemove);
      assertEquals(initialSize - 1, map.size());
    } else {
      try {
        entrySet.remove(entrySet.iterator().next());
        fail("Expected UnsupportedOperationException.");
      } catch (UnsupportedOperationException expected) {
      }
    }

  @CheckForNull
  protected Entry<E> standardFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }
    Entry<E> entry = entryIterator.next();
    return Multisets.immutableEntry(entry.getElement(), entry.getCount());
  }

  @Override
  @CheckForNull
  public Entry<E> lastEntry() {
    return delegate().lastEntry();
  }

  /**

    Entry<String, Collection<Integer>> entry = iterator.next();
    assertEquals("foo", entry.getKey());
    assertThat(entry.getValue()).containsExactly(1, 3, 7);
    entry = iterator.next();
    assertEquals("google", entry.getKey());
    assertThat(entry.getValue()).containsExactly(2, 6);
    entry = iterator.next();
    assertEquals("tree", entry.getKey());

      throws IOException {
    checkNotNull(appendable);
    if (parts.hasNext()) {
      appendable.append(toString(parts.next()));
      while (parts.hasNext()) {
        appendable.append(separator);
        appendable.append(toString(parts.next()));
      }
    }
    return appendable;
  }

  /**

      @Override
      public boolean hasNext() {
        return entryItr.hasNext();
      }

      @Override
      public V next() {
        return entryItr.next().getValue();
      }
    };
  }

  @Override
  public boolean contains(@CheckForNull Object object) {
    return object != null && Iterators.contains(iterator(), object);
  }

  @Override

     * counts are converted to strings as by {@code String.valueOf}.
     */
    @Override
    public String toString() {
      String text = String.valueOf(getElement());
      int n = getCount();
      return (n == 1) ? text : (text + " x " + n);
    }
  }

  /** An implementation of {@link Multiset#equals}. */
  static boolean equalsImpl(Multiset<?> multiset, @CheckForNull Object object) {