@Override
  public boolean isEmpty() {
    return delegate().isEmpty();
  }

  @Override
  public Multiset<K> keys() {
    return delegate().keys();
  }

  @Override
  public Set<K> keySet() {
    return delegate().keySet();
  }

  @CanIgnoreReturnValue
  @Override
  public boolean put(@ParametricNullness K key, @ParametricNullness V value) {
    return delegate().put(key, value);
  }

  @Override
  public boolean isEmpty() {
    return delegate().isEmpty();
  }

  @Override
  public Multiset<K> keys() {
    return delegate().keys();
  }

  @Override
  public Set<K> keySet() {
    return delegate().keySet();
  }

  @CanIgnoreReturnValue
  @Override
  public boolean put(@ParametricNullness K key, @ParametricNullness V value) {
    return delegate().put(key, value);
  }

 * ListMultimap<String, String> multimap = ArrayListMultimap.create();
 * for (President pres : US_PRESIDENTS_IN_ORDER) {
 *   multimap.put(pres.firstName(), pres.lastName());
 * }
 * for (String firstName : multimap.keySet()) {
 *   List<String> lastNames = multimap.get(firstName);
 *   out.println(firstName + ": " + lastNames);
 * }
 * }
 *
 * ... produces output such as:
 *
 * {@snippet :
 * Zachary: [Taylor]

   * interface.
   *
   * @since 14.0 (present with return type {@code SortedSet} since 2.0)
   */
  @Override
  public NavigableSet<K> keySet() {
    return (NavigableSet<K>) super.keySet();
  }

  /**
   * {@inheritDoc}
   *
   * <p>Because a {@code TreeMultimap} has unique sorted keys, this method returns a {@link

                        ArrayTable.create(rowKeys, columnKeys);
                    populateForRowKeySet(table, elements);
                    return table.column(1).keySet();
                  }
                })
            .named("ArrayTable.column.keySet")
            .withFeatures(
                CollectionSize.ONE,
                CollectionSize.SEVERAL,
                CollectionFeature.KNOWN_ORDER,

                        ArrayTable.create(rowKeys, columnKeys);
                    populateForRowKeySet(table, elements);
                    return table.column(1).keySet();
                  }
                })
            .named("ArrayTable.column.keySet")
            .withFeatures(
                CollectionSize.ONE,
                CollectionSize.SEVERAL,
                CollectionFeature.KNOWN_ORDER,

      String value2 = key2.toString();
      assertThat(cache.getUnchecked(key1)).isSameInstanceAs(value1);
      assertThat(cache.getUnchecked(key2)).isSameInstanceAs(value2);
      assertThat(cache.asMap().keySet()).isEqualTo(ImmutableSet.of(key1, key2));
      assertThat(cache.asMap().values()).containsExactly(value1, value2);
      assertThat(cache.asMap().entrySet())

    }

    @LazyInit private transient @Nullable Set<K> keySet;

    @Override
    public Set<K> keySet() {
      Set<K> result = keySet;
      return (result == null) ? keySet = createKeySet() : result;
    }

    Set<K> createKeySet() {
      return new KeySet<>(this);
    }

    @LazyInit private transient @Nullable Collection<V> values;

          }
        }
        return endOfData();
      }
    }

    @Override
    Set<R> createKeySet() {
      return new KeySet();
    }

    @WeakOuter
    private final class KeySet extends Maps.KeySet<R, V> {
      KeySet() {
        super(Column.this);
      }

      @Override
      public boolean contains(@Nullable Object obj) {

      synchronized (mutex) {
        delegate().clear();
      }
    }

    @Override
    public Set<K> keySet() {
      synchronized (mutex) {
        if (keySet == null) {
          keySet = typePreservingSet(delegate().keySet(), mutex);
        }
        return keySet;
      }
    }

    @Override
    public Collection<V> values() {
      synchronized (mutex) {