QCD Analysis of Inclusive $\Delta S=1,2$ Transitions: The $|\Delta   I|=1/2$ Rule
  The interplay of QCD in $\Delta S=1,2$ non-leptonic weak transitions can be rigorously analyzed, at the inclusive level, by studying the 2--point functions associated with the corresponding $\Delta S=1,2$ effective Hamiltonians. The next-to-leading order calculation of these correlators shows a huge ($\gsim 100\%$) gluonic enhancement of the $|\Delta I|=1/2$ channel, providing a qualitative understanding of the $|\Delta I|=1/2$ rule within QCD. 
A. Pich