The definition of the response functions is fully consistent with D. Drechsel and L. Tiator, J. Phys. G 18 (1992) 449-497 and G. Knoechlein, D. Drechsel, L. Tiator, Z. Phys. A 352 (1995) 327-343 Care must be taken in respect to the coordinate systems in which the target and the recoil polarization vectors are defined. (See further details about polarization) When calculating 2-fold and 5-fold coincidence cross sections the response functions must be multiplied a) with the phase space factor (q/k_gam), where q is the pion momentum and k_gam is the photon equivalent energy in the cm frame b) with a factor (Q/omega) for each longitudinal component, e.g. (Q^2/omega^2) for sig_L (Q/omega) for sig_LT and sig_LT' c) with the appropriate epsilon factors when a virtual cross section or a 5-fold cross section is wanted Note: Here we do not use epsilon_L !!!