Write down one of the three contraction terms in (9-3), other than (B9-1.1) and (B9-1.2) of Box 9-1 on pg. 258, that has two fermion contractions and one photon contraction. Re-arrange it by commuting/anti-commuting fields until it looks like (B9-1.1), except with event labels xi in different order. In an integral over all three xi, do we just change the variable labels to look identical to (B9-1.1)?