  The availaible data on the D0 to K0S pi+ pi- decays are analysed in the
framework of the quasi two-body QCD factorization approximation. The
annihilation, via W-exchange, amplitudes are added to the weak-decay tree
amplitudes. The doubly Cabibbo suppressed parts of the amplitudes are also
considered. The strong interactions between the kaon-pion and pion-pion pairs
in the S-, P- and D-final states are described in terms of the corresponding
form factors. The kaon-pion or pion-pion scalar and vector form factors are
constrained by other experimental data. Unitarity, analyticity and chiral
symmetry are also used to obtain their functional forms. We go through a
minimization procedure to reproduce the K0S pi-, K0S pi+ and pi+ pi- effective
mass projections of the Dalitz plot distributions. The large number (27) of
non-zero amplitudes leads to a large number of parameters. The resulting model
distributions and branching fractions are compared to the accurate Belle
Collaboration data.
