(skipping the terms proportional to S 2 and S 0 ), we obtain the P4 operator (after accounting for the correct prefactor). This action can be formally obtained by taking a normal order of second-quantized operators in expression (20) with respect to both physical vacuums of monomers A and B. Then, by taking a product P4 P2 and proceeding similarly, it is possible to construct a P6 operator. Repeating this procedure n -1 times a proper form of the P2n