Physics of weak nonleptonic decays:K→ππ

We evaluate long-distance effects in $K\to \pi \pi$ decays using a calculational scheme based on partial conservation of axial-vector current, current algebra, and suppression of exotic Regge meson trajectories. We find that the $\Delta I=\frac{1}{2}$ rule emerges naturally from these properties of hadronic physics. Moreover the calculated long-distance contributions are seen to play the dominant role, as opposed to short-distance effects.