  The inclusion of electromagnetism in a low energy effective theory is worth
further study in view of the present high precision experiments (muon g-2,
pi_0->2 gamma, tau decays, etc.). In particular in many applications of chiral
perturbation theory, one has to purify physical matrix elements from
electromagnetic effects. The theoretical problems that I want to point out here
are following: the splitting of a pure QCD and a pure electromagnetic part in a
hadronic process is model dependent: is it possible to parametrise in a clear
way this splitting? What kind of information (scale dependence, gauge
dependence,..) is actually included in the parameters of the low energy
effective theory? I will attempt to answer these questions introducing a
possible convention to perform the splitting between strong and electromagnetic
parts in some examples.
