Explicit generating functional for pions and virtual photons

We construct the explicit one-loop functional of chiral perturbation theory for two light flavours, including virtual photons. We stick to contributions where 1 or 2 mesons and at most one photon are running in the loops. With the explicit function a lath and, the evaluation of the relevant Green functions boils down to performing traces over the flavour matrices. For illustration, we work out the pi(+)pi(-) --> pi(0)pi(0) scattering amplitude at threshold at order p(4), e(2)p(2).