assertThrows(NoSuchElementException.class, () -> navigableMap.firstKey());
  }

  @CollectionSize.Require(ZERO)
  public void testEmptyMapLast() {
    assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapFirst() {
    assertEquals(a.getKey(), navigableMap.firstKey());
  }

  @CollectionSize.Require(ONE)

    assertThrows(NoSuchElementException.class, () -> navigableMap.firstKey());
  }

  @CollectionSize.Require(ZERO)
  public void testEmptyMapLast() {
    assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapFirst() {
    assertEquals(a.getKey(), navigableMap.firstKey());
  }

  @CollectionSize.Require(ONE)

      return new TreeRow(rowKey, fromKey, upperBound);
    }

    @Override
    public C firstKey() {
      updateBackingRowMapField();
      if (backingRowMap == null) {
        throw new NoSuchElementException();
      }
      return ((SortedMap<C, V>) backingRowMap).firstKey();
    }

    @Override
    public C lastKey() {
      updateBackingRowMapField();

    TreeMultimap<String, Integer> multimap = createPopulate();
    SortedMap<String, Collection<Integer>> asMap = multimap.asMap();
    assertEquals(Ordering.natural(), asMap.comparator());
    assertEquals("foo", asMap.firstKey());
    assertEquals("tree", asMap.lastKey());
    Set<Integer> fooValues = ImmutableSet.of(1, 3, 7);
    Set<Integer> googleValues = ImmutableSet.of(2, 6);
    Set<Integer> treeValues = ImmutableSet.of(4, 0);

    @Override
    @CheckForNull
    public Comparator<? super K> comparator() {
      return fromMap().comparator();
    }

    @Override
    @ParametricNullness
    public K firstKey() {
      return fromMap().firstKey();
    }

    @Override
    public SortedMap<K, V2> headMap(@ParametricNullness K toKey) {
      return transformEntries(fromMap().headMap(toKey), transformer);
    }

    @Override
    @CheckForNull
    public Comparator<? super K> comparator() {
      return fromMap().comparator();
    }

    @Override
    @ParametricNullness
    public K firstKey() {
      return fromMap().firstKey();
    }

    @Override
    public SortedMap<K, V2> headMap(@ParametricNullness K toKey) {
      return transformEntries(fromMap().headMap(toKey), transformer);
    }

  }

  public void testRowMapFirstKey() {
    sortedTable = create("foo", 1, 'a', "bar", 1, 'b', "foo", 3, 'c');
    assertSame("bar", sortedTable.rowMap().firstKey());
  }

  public void testRowMapLastKey() {
    sortedTable = create("foo", 1, 'a', "bar", 1, 'b', "foo", 3, 'c');
    assertSame("foo", sortedTable.rowMap().lastKey());
  }

    public Comparator<? super K> comparator() {
      synchronized (mutex) {
        return delegate().comparator();
      }
    }

    @Override
    public K firstKey() {
      synchronized (mutex) {
        return delegate().firstKey();
      }
    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      synchronized (mutex) {

    public Comparator<? super K> comparator() {
      synchronized (mutex) {
        return delegate().comparator();
      }
    }

    @Override
    public K firstKey() {
      synchronized (mutex) {
        return delegate().firstKey();
      }
    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      synchronized (mutex) {

      replica.put(newValue, new AtomicInteger(1));
    }
  }

  private static void removeMinFromReplica(
      SortedMap<Integer, AtomicInteger> replica, int minValue) {
    Integer replicatedMinValue = replica.firstKey();
    assertEquals(replicatedMinValue, (Integer) minValue);
    removeFromReplica(replica, replicatedMinValue);
  }

  private static void removeMaxFromReplica(