On the large-Nc behaviour of the L7 coupling in Χpt

It is shown that the usual large-Nc counting of the coupling constant L7 of the O(p4) low-energy chiral SU(3) Lagrangian [J. Gasser and H. Leutwyler, Nucl. Phys. B 250 (1985) 465, 517, 539] is in conflict with general properties of QCD in the large-Nc limit. The solution of this conflict within the framework of a chiral U(3) Lagrangian is explained.