private static void handleBitSet(BitSet orig, BitSet copy, BitSet removed) {
		if (orig.cardinality() <= 0)
			return;
		if (copy == null) {
			copy = new BitSet(orig.size());
		}
		else {
			copy.clear();
		}
		int n = orig.length();
		int m = 0;
		for (int i = 0; i < n; i++) {
			if (removed.get(i))
				continue;
			copy.set(m++, orig.get(i));
		}
		copyBitSet(copy, orig);
	}