equation icon  pa(u) = ga ua'ub'+ ga aa' [ a';b' a' ] a 1- a b 2 a = a + 2rR 0b0_O_ + O(r ) ea, ' ' ' ( ' ' ' ') ' ¨pa(u) = gaa';b'g'ua ub ug + gaa';b' 2aa ub + ua ab + gaa'aa a a a = [- a0 + O(r)] e0 + [a + O(r)]ea ,