  A recently proposed strategy to quantify the role of the charm quark mass in
the $\Delta I=1/2$ rule is reviewed. Results for the low-energy couplings of
the $\Delta S=1$ chiral effective Hamiltonian in a theory with a light charm
quark (GIM limit) are obtained through a matching of three-point correlation
functions computed in Chiral Perturbation Theory and in quenched lattice QCD.
We observe a large $\Delta I=1/2$ enhancement, which is not large enough to
explain the experimental result, but suggests significant long-distance
contributions to the physical $\Delta I=1/2$ which are unrelated to penguin
contractions or operators.
