  By using only combinatorial data on two posets X and Y, we construct a set of
so-called formulas. A formula produces simultaneously, for any abelian category
A, a functor between the categories of complexes of diagrams over X and Y with
values in A. This functor induces a triangulated functor between the
corresponding derived categories.
  This allows us to prove, for pairs X, Y of posets sharing certain common
underlying combinatorial structure, that for any abelian category A, regardless
of its nature, the categories of diagrams over X and Y with values in A are
derived equivalent.
