Composite operators as integration variables in Berezin integrals

We define nonlinear changes of variables in Berezin integrals, assuming as new integration variables multilinear functions of the defining elements of the Grassmann algebra. We apply such a change of variables to QCD by introducing as integration variables trilinear and bilinear functions of the quark field, with the quantum numbers of the nucleon and the meson respectively, and we suggest a perturbative scheme using these functions as free states. ((orig.))