  We review our recent analysis of pion-pion scattering data in terms of Roy
equations and Forward Dispersion Relations, and present some preliminary
results in terms of a new set of once-subtracted coupled equations for partial
waves. The first analysis consists of independent fits to the different
pion-pion channels that satisfies rather well the dispersive representation. In
the second analysis we constrain the fit with the dispersion relations. The
latter provides a very precise and model independent description of data using
just analyticity, causality and crossing.
