1485In the framework of tree approximation, the soft-pion theorems are shown to hold true even in a general case where 1 ± meson fields are contained in the chiral invariant Lagrangian, which is applicable to hard-pion processes. Thus, contrary to the results of Biswas et al. forKl4 decays, we are led to almost the same results as those of the soft-pion technique when re-examining their calculations. § 1. IntroductionRecently, Dashen and W einstein 1 ) have shown that the soft-pion theorem is justified by an assumption that the real world satisfies an approximate chiral symmetry and, moreover, in the symmetry limit the pion behaves as a Goldstone boson. Starting only from the above assumption, they have also derived a phenomenological Lagrangian which, in the tree approximation, must give the same results as the full theory when calculating the leading order in pion momenta of any amplitudes. This Lagrangian is essentially the same as the one proposed by Weinberg and Schwinger et al.,2 ) and the characteristic feature of this Lagrangian is that o-mesons couple with other hadrons only through phenomenological currents built out of the external hadrons.On the other hand, many authors 3 ) have studied low energy phenomena, including hard-pion processes, by means of various approximately chiral invariant Lagrangians which contain explicitly vector (1-) and axial-vector (1 +) · mesons and other hadrons. These are not contained in the framework of the effective Lagrangian derived by Dashen and W einstein. 1 ) In the course of their calculations, they have considered from the outset tree diagrams only, instead of taking account of the whole diagrams.In this respect, there arises a non-trivial question as to whether we can again obtain the soft-pion theorems even when we take an arbitrary chiral invariant Lagrangian explicitly containing 1 ± mesons and calculate tree diagrams only. For the observation of Dashen and Weinstein is that, if the original Lagrangian is solved by calculating the whole diagrams, the results are equivalent in the leading order of pion momenta to those obtained from the phenomenological one in the at Ernst Mayr