  Stimulated by recent T2K indications on a surprisingly large neutrino mixing
theta_13 angle we suggest that this last unknown angle is not independent but
determined by the known large solar and atmospheric neutrino oscillation angles
via simple, symmetric, positive-definite equation. Encouragingly, it appears in
agreement with recent new long base-line appearance nu-mu to nu-e neutrino
oscillation T2K data. At zero approximation this equation determines benchmark
bimaximal neutrino mixing matrix as its unique solution with one texture zero.
Extension to quark mixing angles leads to definite equation with unit mixing
matrix as sole solution. All six realistic neutrino and quark mixing angles are
explicitly expressed as small deviations from the zero approximation benchmark
ones by one small empirical universal parameter. Thus in the considered
semi-empirical flavor phenomenology the system of two related neutrino and
quark equations is the source of the known main empirical rule of 'large
neutrino mixing angles versus small quark ones' as well as other particle
mixing regularities.
