public StandardNavigableKeySet() {
      super(ForwardingNavigableMap.this);
    }
  }

  @Override
  public NavigableSet<K> descendingKeySet() {
    return delegate().descendingKeySet();
  }

  /**
   * A sensible definition of {@link #descendingKeySet} as the {@code navigableKeySet} of {@link
   * #descendingMap}. (The {@link StandardDescendingMap} implementation implements {@code

    public StandardNavigableKeySet() {
      super(ForwardingNavigableMap.this);
    }
  }

  @Override
  public NavigableSet<K> descendingKeySet() {
    return delegate().descendingKeySet();
  }

  /**
   * A sensible definition of {@link #descendingKeySet} as the {@code navigableKeySet} of {@link
   * #descendingMap}. (The {@link StandardDescendingMap} implementation implements {@code

    }
  }

  @Override
  public boolean containsValue(Object value) {
    return delegate.containsValue(value);
  }

  @Override
  public NavigableSet<K> descendingKeySet() {
    return delegate.descendingKeySet();
  }

  @Override
  public NavigableMap<K, V> descendingMap() {
    return new SafeTreeMap<>(delegate.descendingMap());
  }

  @Override

    }
  }

  @Override
  public boolean containsValue(Object value) {
    return delegate.containsValue(value);
  }

  @Override
  public NavigableSet<K> descendingKeySet() {
    return delegate.descendingKeySet();
  }

  @Override
  public NavigableMap<K, V> descendingMap() {
    return new SafeTreeMap<>(delegate.descendingMap());
  }

  @Override

    return new Maps.NavigableKeySet<>(this);
  }

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

  @Override
  public NavigableSet<K> descendingKeySet() {
    return descendingMap().navigableKeySet();
  }

  @Override
  public NavigableMap<K, V> descendingMap() {
    return new DescendingMap();
  }

    return new Maps.NavigableKeySet<>(this);
  }

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

  @Override
  public NavigableSet<K> descendingKeySet() {
    return descendingMap().navigableKeySet();
  }

  @Override
  public NavigableMap<K, V> descendingMap() {
    return new DescendingMap();
  }

      }
    }

    transient @Nullable NavigableSet<K> descendingKeySet;

    @Override
    public NavigableSet<K> descendingKeySet() {
      synchronized (mutex) {
        if (descendingKeySet == null) {
          return descendingKeySet = Synchronized.navigableSet(delegate().descendingKeySet(), mutex);
        }
        return descendingKeySet;
      }
    }

      }
    }

    transient @Nullable NavigableSet<K> descendingKeySet;

    @Override
    public NavigableSet<K> descendingKeySet() {
      synchronized (mutex) {
        if (descendingKeySet == null) {
          return descendingKeySet = Synchronized.navigableSet(delegate().descendingKeySet(), mutex);
        }
        return descendingKeySet;
      }
    }

    }

    @Override
    public NavigableSet<K> navigableKeySet() {
      return new StandardNavigableKeySet();
    }

    @Override
    public NavigableSet<K> descendingKeySet() {
      return standardDescendingKeySet();
    }

    @Override
    public K firstKey() {
      return standardFirstKey();
    }

    @Override

    @Override
    public @Nullable K ceilingKey(@ParametricNullness K key) {
      return fromMap().ceilingKey(key);
    }

    @Override
    public NavigableSet<K> descendingKeySet() {
      return fromMap().descendingKeySet();
    }

    @Override
    public NavigableMap<K, V2> descendingMap() {
      return transformEntries(fromMap().descendingMap(), transformer);
    }

    @Override