Hi, Halzen and Martin, on page 18 of their book, describe the resolution of hadron structure using virtual photons obtained by annihilating e+ and e- beams. In Figure 1.11(b), isn't the positron arrow shown wrongly? It seems to be moving forward in time. (Or maybe I'm just being picky here?) They go on to say, What does "produced at rest" mean? Thanks in advance!