  Two body data alone cannot determine the potential uniquely, one needs
three-body data as well. A method is presented here which simultaneously fits
local or nonlocal potentials to two-body and three-body observables. The
interaction of composite particles, due to the Pauli effect and the
indistinguishability of the constituent particles, is genuinely nonlocal. As an
example, we use a Pauli-correct nonlocal fish-bone type optical model for the
$\alpha-\alpha$ potential and derive the fitting parameters such that it
reproduces the two-$\alpha$ and three-$\alpha$ experimental data.
