ContiguousSet<C> headSetImpl(C toElement, boolean inclusive) {
    return this;
  }

  @Override
  ContiguousSet<C> subSetImpl(
      C fromElement, boolean fromInclusive, C toElement, boolean toInclusive) {
    return this;
  }

  @Override
  ContiguousSet<C> tailSetImpl(C fromElement, boolean fromInclusive) {
    return this;
  }

  @Override
  public boolean contains(@Nullable Object object) {
    return false;
  }

      public SortedSet<E> subSet(
          @ParametricNullness E fromElement, @ParametricNullness E toElement) {
        return removeOnlySortedSet(super.subSet(fromElement, toElement));
      }

      @Override
      public SortedSet<E> tailSet(@ParametricNullness E fromElement) {
        return removeOnlySortedSet(super.tailSet(fromElement));
      }
    };
  }

  @GwtIncompatible // NavigableSet

      public SortedSet<E> subSet(
          @ParametricNullness E fromElement, @ParametricNullness E toElement) {
        return removeOnlySortedSet(super.subSet(fromElement, toElement));
      }

      @Override
      public SortedSet<E> tailSet(@ParametricNullness E fromElement) {
        return removeOnlySortedSet(super.tailSet(fromElement));
      }
    };
  }

  @GwtIncompatible // NavigableSet

  public SortedMultiset<E> subMultiset(
      @ParametricNullness E fromElement,
      BoundType fromBoundType,
      @ParametricNullness E toElement,
      BoundType toBoundType) {
    // These are checked elsewhere, but NullPointerTester wants them checked eagerly.
    checkNotNull(fromBoundType);
    checkNotNull(toBoundType);
    return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
  }

    }

    @Override
    public NavigableSet<E> tailSet(@ParametricNullness E fromElement, boolean inclusive) {
      return forward.headSet(fromElement, inclusive).descendingSet();
    }

    @Override
    public SortedSet<E> tailSet(@ParametricNullness E fromElement) {
      return standardTailSet(fromElement);
    }

    @SuppressWarnings("unchecked")
    @Override