boolean isSubset( BitSet bs1, BitSet bs2 )
    {
        for ( int i = bs1.nextSetBit(0);i>=0;i=bs1.nextSetBit(i+1) ) 
            if ( bs2.nextSetBit(i)!=i )
                return false;
        return true && bs2.cardinality()>bs1.cardinality();
    }