Separated presentations of modules over pullback rings

We define pullback and separated presentations of modules over pullback rings, and, if the ring is a pullback of epimorphisms over a semisimple ring, an algorithm reducing such a presentation of a module to an $R$-diagram. The latter is the input for a classification algorithm of finitely generated modules over a pullback ring of two Dedekind domains. As an example we show how to obtain an $R$-diagram for homology of a chain complex of free modules over a $p$-pullback ring.