Twopion decays of K mesons, K_L-K_S mass difference and the Dalitz decays of K_L

Two pion Decays of K mesons, K_L-K_S mass difference, two photon decay and the Dalitz decays of K_L are studied systematically by assuming that their amplitude can be described in terms of a sum of short distance and long distance contributions. Dominance of the short distance effect on the K_L-K_S mass difference will be checked by the Dalitz decays of K_L in a way consisten with the two pion decays of K mesons and the two photon decay of K_L.