equation icon  [ ] [ ] a 1 b 2 a 1 b c 2 a p a(t) = aa + 2sRa0b0w + O(s ) e0 + - 2-sR a0cw + O(s ) eb, [ ] p¨aa(t) = [aa + O(s)]ea0 + aaab + O(s) eab,