  The flavor SU(3)_f group symmetry of QCD is systematically considered as the
heavy c quark limit of SU(4)_f. Within that scheme we argue that the U(1)_A
anomaly prevents Gell-Mann's choice for the realization of the su(4)_f (and
thereby the su(3)_f) algebra for the particular case of the neutral axial
currents. Rather, Weyl's choice for the SU(4)_f generators has to be used which
leads to a neutral strong axial current having same structure (up to a constant
factor) as the weak one.
