equation icon  { } t = u + r 1- raa(u)_O_a + r2 [aa(u)_O_a]2 - 1r2a0(u) - 1r2aa(u)_O_a - 1-r2Ra0b0(u)_O_a_O_b + O(r3) , 3 2 3 (218)