equation icon  { 1 [ ] 1 1 1 } swa = r _O_a - -r 1- rab(u)_O_b aa(u)- -r2aa(u) - --r2Ra0b0(u)_O_b + --r2Rab0c(u)_O_b_O_c+ O(r3) 2 6 6 3 (219)