}

    @Override
    public Iterator<Set<E>> iterator() {
      return new AbstractIndexedListIterator<Set<E>>(size()) {
        @Override
        protected Set<E> get(final int setBits) {
          return new SubSet<>(inputSet, setBits);
        }
      };
    }

    @Override
    public boolean contains(@CheckForNull Object obj) {
      if (obj instanceof Set) {
        Set<?> set = (Set<?>) obj;

    }
  }

  @GwtIncompatible // TODO
  public void testConstantMaxPowerOfSqrt2Unsigned() {
    assertEquals(
        /*expected=*/ BigIntegerMath.sqrt(BigInteger.ZERO.setBit(2 * Long.SIZE - 1), FLOOR)
            .longValue(),
        /*actual=*/ LongMath.MAX_POWER_OF_SQRT2_UNSIGNED);
  }

  @GwtIncompatible // BigIntegerMath // TODO(cpovirk): GWT-enable BigIntegerMath

    doTestSetBits(inRange('A', 'Z').and(inRange('F', 'K').negate()));
  }

  @GwtIncompatible // java.util.BitSet
  private void doTestSetBits(CharMatcher matcher) {
    BitSet bitset = new BitSet();
    matcher.setBits(bitset);
    for (int i = Character.MIN_VALUE; i <= Character.MAX_VALUE; i++) {
      assertEquals(matcher.matches((char) i), bitset.get(i));
    }
  }

  public void testEmpty() throws Exception {

    doTestSetBits(inRange('A', 'Z').and(inRange('F', 'K').negate()));
  }

  @GwtIncompatible // java.util.BitSet
  private void doTestSetBits(CharMatcher matcher) {
    BitSet bitset = new BitSet();
    matcher.setBits(bitset);
    for (int i = Character.MIN_VALUE; i <= Character.MAX_VALUE; i++) {
      assertEquals(matcher.matches((char) i), bitset.get(i));
    }
  }

  public void testEmpty() throws Exception {

    }
  }

  @GwtIncompatible // TODO
  public void testConstantMaxPowerOfSqrt2Unsigned() {
    assertEquals(
        /*expected=*/ BigIntegerMath.sqrt(BigInteger.ZERO.setBit(2 * Long.SIZE - 1), FLOOR)
            .longValue(),
        /*actual=*/ LongMath.MAX_POWER_OF_SQRT2_UNSIGNED);
  }

  @GwtIncompatible // BigIntegerMath // TODO(cpovirk): GWT-enable BigIntegerMath