On the validity of chiral perturbation theory for the ΔI= 1 2 rule
The chiral perturbation theory relations of 〈ππ|O|K〉 to 〈π|O|K〉 and 〈o|O|K〉 needed for establishing the ΔI= 1 2 rule in hadronic weak decays via lattice calculations are examined beyond leading order and the domain of validity for this relation is established.