Murph and I did a variety of things. One was we noticed the crossing relations, coming from the fact that diagrams would always have symmetry between crossed and uncrossed lines. And that gave rise to a symmetry in the relativistic scattering amplitudes in which one interchanged positive and negative momenta and so on and so forth, as you know. So these crossing relations we discovered, we never really wrote them up. We referred to them in various things that we wrote, but we never actually wrote them up as a discovery. Another example of this business of not taking important things seriously, if… if we had done them or if I had done them. Now of course the old-timers in quantum mechanics knew about  such as symmetry vaguely. It was a kind of folk theorem. They never wrote it down either, and they never used it for anything much, but they did know that there was such a thing, even in the old-fashioned form of quantum field theory. Another thing we did then was to look at forward scattering amplitudes for massless particles, say a photon, so, forward photon scattering, and return to the old work on dispersion relations which had given rise to quantum mechanics in the work of Kramers, Heisenberg, Born and so on, in 1924–just before quantum mechanics. And we showed that there were these forward scattering dispersion relations. We found a new one for spin flip with the opposite crossing symmetry, and then later on Murph and some collaborators showed that there were these relations even when you didn't have a massless particle like the photon. And then Polkinghorne and I, and a great number of other people, showed that you would have them also for non-forward scattering, for fixed momentum transfer. That was very exciting because all of this work was on the mass shell.