We discuss the renormalisation group (RG) evolution for the Δ S = 1 operators in unquenched QCD with N_f = 3 (m_u=m_d=m_s) or, more generally, N_f = 2+1 (m_u=m_d m_s) flavors. In particular, we focus on the specific problem of how to treat the singularities which show up only for N_f=3 or N_f = 2+1 in the original solution of Buras et al. for the RG evolution matrix at next-to-leading order. On top of Buras et al.'s original treatment, we use a new method of analytic continuation to obtain the

more »

... orrect solution in this case. It is free of singularities and can therefore be used in numerical analysis of data sets calculated in lattice QCD.