This is the first of a series of papers on a consistent model independent analysis of the complete experimental information on the reaction πN → ππN at pion momenta up to 500 MeV/c. The paper summarizes the theoretical approach and details of the computational procedure. The complete database on total cross sections in 5 ππN channels is given together with a critical discussion of their model independent analysis. * This work was funded by the Deutsche Forschungsgemeinschaft (DFG), Bundesminister für Forschung und Technologie (BMFT), and the Kernforschungsanlage Jülich (KFA) and Russian Ministry of Education Grant G13.018 0

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The first kinematically complete, good-statistics data for the {n.ln) reaction on the proton are presented. They involve double-and triple-differential cross sections as well as K^7t~ angular correlations. At energies around the A resonance, they exhibit a marked difference from phase space. The data are qualitatively described within the framework of an extension of Weinberg's effective chiral Lagrangian.PACS numbers: 13.75.Gx, lI.40.Fy, 13.75.LbThe nN interaction at medium energies is beyond the scope of perturbative QCD, since it is dominated by confinement. However, on a less fundamental level, the symmetries of QCD guide the formulation of effective Lagrangians. Among other symmetries, the importance of chiral symmetry has been increasingly realized in recent years.' The resulting chiral Lagrangians involve highly nonlinear contributions in the pion field, as already realized in the nonlinear

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