Z_{{{R}_{j}}}^{\left( {{\pi }_{S}} \right)}\left( \left( {{R}_{i}},{{\sigma }_{k}} \right) \right) \right)\left( Z_{{{R}_{j}}}^{\left( {{{{\pi }'_{S}}}} \right)}\left( \left( {{R}_{i}},{{\sigma }_{k}} \right) \right)+Z_{{{R}_{j}}}^{\left( {{\pi }_{S}} \right)}\left( \left( {{R}_{i}},{{\sigma }_{k}} \right) \right) \right)