  Suppose given a Frobenius category E, i.e. an exact category with a big
enough subcategory B of bijectives. Let_E_ := E/B denote its classical stable
category. For example, we may take E to be the category of complexes C(A) with
entries in an additive category A, in which case_E_ is the homotopy category of
complexes K(A). Suppose given a finite poset D that satisfies the combinatorial
condition of being ind-flat. Then, given a diagram of shape D with values in_E_
(i.e. commutative up to homotopy), there exists a diagram consisting of pure
monomorphisms with values in E (i.e. commutative) that is isomorphic, as a
diagram with values in_E_, to the given diagram.
