  Let R be a local ring and A a connected differential graded algebra over R
which is free as a graded R-module. Using homological perturbation theory
techniques, we construct a minimal free multi model for A having properties
similar to that of an ordinary minimal model over a field; in particular the
model is unique up to isomorphism of multialgebras. The attribute multi refers
to the category of multicomplexes.

Algebraic Topology