equation icon  [ ] [ ] swa = r_O_a - r aa + 1rSa + O(r2) D + 1- (1 + ra _O_b)aa - raa + 1rRa _O_b + O(r2) D2 3 2 b 3 0b0 1 + --[aa + O(r)]D3 + O(D4), 3