"Bhabha scattering 2" E = sqrt(p^2 + m^2) p1 = (E, 0, 0, p) p2 = (E, 0, 0, -p) p3 = (E, p sin(theta) cos(phi), p sin(theta) sin(phi), p cos(theta)) p4 = (E, -p sin(theta) cos(phi), -p sin(theta) sin(phi), -p cos(theta)) check(p4 + p3 - p2 - p1 == 0) "ok" Run