This paper presents a systematic approach to determine the low energy structure of Green's functions in Quantum Chromodynamics (QCD) by expanding in the mass of the strange quark. The authors construct a generating functional for the U(3)×U(3) symmetry that allows the calculation of all Green's functions up to order p⁴ in terms of a few coupling constants, which are not fixed by experimental low energy information. These constants are estimated using large Nₐ arguments. The paper extends previous work on chiral symmetry breaking in QCD to include the strange quark mass. The authors calculate the first non-leading terms in the quark mass expansion of order parameters and masses and decay constants in the pseudoscalar octet. They also discuss the role of the n' meson in chiral perturbation theory and the implications of large Nₐ and the Zweig rule. The effective low energy Lagrangian is derived, and the ground state is analyzed. The paper also addresses the low energy expansion at leading order and the effective Lagrangian to order p⁴. The authors show how to calculate the first non-leading contributions in a systematic manner and discuss the implications of the results for the low energy structure of QCD. The paper concludes with a summary of the results and their significance for understanding the low energy behavior of QCD.This paper presents a systematic approach to determine the low energy structure of Green's functions in Quantum Chromodynamics (QCD) by expanding in the mass of the strange quark. The authors construct a generating functional for the U(3)×U(3) symmetry that allows the calculation of all Green's functions up to order p⁴ in terms of a few coupling constants, which are not fixed by experimental low energy information. These constants are estimated using large Nₐ arguments. The paper extends previous work on chiral symmetry breaking in QCD to include the strange quark mass. The authors calculate the first non-leading terms in the quark mass expansion of order parameters and masses and decay constants in the pseudoscalar octet. They also discuss the role of the n' meson in chiral perturbation theory and the implications of large Nₐ and the Zweig rule. The effective low energy Lagrangian is derived, and the ground state is analyzed. The paper also addresses the low energy expansion at leading order and the effective Lagrangian to order p⁴. The authors show how to calculate the first non-leading contributions in a systematic manner and discuss the implications of the results for the low energy structure of QCD. The paper concludes with a summary of the results and their significance for understanding the low energy behavior of QCD.