2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/198703We report on some recent progress made in understanding weak matrix elements of mesons in the context of the next-to-leading order of the large-Nc approximation to QCD. Specifically, we first use the example of the weak contributions to the pi^+ - pi^0 mass difference to exhibit how a systematic matching can be achieved analytically between short distances and long distances within our large-Nc framework. We are then also able to compute matrix elements of the operator Q_7, as they turn out to depend on the same QCD correlator as the previous pion mass difference. As a final example we determine the chiral counterterms governing the pseudoscalar decay into a lepton pair, where we briefly comment also on the special case K_L -> mu^+ mu^-.15 pages, 4 figures. LateX. This report covers the material presented by the authors in three separate talks at the QCD'99 conference in MontpellierHigh Energy Physics - Phenomenologytext