Equation Icon  [ ] 1 ( ) [ ] 1( ) σ αβγδ = − -- Rα′γ′β′δ′ + R α′δ′β′γ′ , σαβγδ′ = --R α′γ′β′δ′ + Rα′δ′β′γ′, [ ] 3 ( ) [ ] 3 ( ) σ αβγ′δ′ = − 1- Rα′γ′β′δ′ + R α′δ′β′γ′ , σαβ′γ′δ′ = − 1-R α′β′γ′δ′ + R α′γ′β′δ′ , 3 3 [ ] 1-( ) σα ′β′γ′δ′ = − 3 Rα′γ′β′δ′ + R α′δ′β′γ′ . (4.5 )