/**
     * Delegates to each filter in the chain.
     * @param reader IndexReader
     * @param logic Logical operation
     * @return BitSet
     */
    private BitSet bits(IndexReader reader, int logic) throws IOException
    {
        BitSet result;
        int i = 0;

        /**
         * First AND operation takes place against a completely false
         * bitset and will always return zero results. Thanks to
         * Daniel Armbrust for pointing this out and suggesting workaround.
         */
        if (logic == AND)
        {
            result = (BitSet) chain[i].bits(reader).clone();
            ++i;
        }
+       else
+       if (logic == ANDNOT)
+       {
+       	result = (BitSet) chain[i].bits(reader).clone();
+          	result.flip(0,reader.maxDoc());
+           ++i;
+       }
        else
        {
            result = new BitSet(reader.maxDoc());
        }

        for (; i < chain.length; i++)
        {
            doChain(result, reader, logic, chain[i]);
        }
        return result;
    }

    /**
     * Delegates to each filter in the chain.
     * @param reader IndexReader
     * @param logic Logical operation
     * @return BitSet
     */
    private BitSet bits(IndexReader reader, int[] logic) throws IOException
    {
        if (logic.length != chain.length)
            throw new IllegalArgumentException("Invalid number of elements in logic array");
        BitSet result;
        int i = 0;

        /**
         * First AND operation takes place against a completely false
         * bitset and will always return zero results. Thanks to
         * Daniel Armbrust for pointing this out and suggesting workaround.
         */
        if (logic[0] == AND)
        {
            result = (BitSet) chain[i].bits(reader).clone();
            ++i;
        }
+       else
+       if (logic[0] == ANDNOT)
+       {
+           result = (BitSet) chain[i].bits(reader).clone();
+           result.flip(0,reader.maxDoc());
+           ++i;
+       }
        else
        {
            result = new BitSet(reader.maxDoc());
        }

        for (; i < chain.length; i++)
        {
            doChain(result, reader, logic[i], chain[i]);
        }
        return result;
    }