Effective interactions through core polarization have been shown to undergo drastic changes by taking particular higher order terms as a vertex modification. 0 Therein even the qualitative features of second-order perturbational or RP A results are not conserved. In this note we show that results are stabilized, if we carry out exact antisymmetrization between valence and core-excited nucleons. In the vertexmodification approximation antisymmetrization is taken into account only partially. We

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... nstruct multiple scattering equations for (2p-lh) system (one valence nucleon plus' one core-excited particle-hole), which contain all-order interactions between three pairs an tisymmetrized in every step: