  For reliable comparison of the standard model prediction to the muon g-2 with
its experimental value, the hadronic light-by-light scattering (HLbL)
contribution must be calculated by lattice QCD simulation. HLbL contribution
has many types of disconnected-type diagrams. Here, we start with recalling the
point that must be taken care of in every method to calculate them by lattice
QCD, and present one concrete method called nonperturbative QED method.
