  Azimuthal single-spin asymmetries of lepto-produced pions and charged kaons
were measured on a transversely polarized hydrogen target. Evidence for a
naive-T-odd, transverse-momentum-dependent parton distribution function is
deduced from non-vanishing Sivers effects for pi+, pi0, and K+, K-, as well as
in the difference of the pi+ and pi- cross sections.
