The homology digraph of a preordered space

This paper studies a notion of directed homology for preordered spaces, called the homology digraph. We show that the homology digraph is a directed homotopy invariant and establish variants of the main results of ordinary singular homology theory for the homology digraph. In particular, we prove a K\"unneth formula, which enables one to compute the homology digraph of a product of preordered spaces from the homology digraphs of the components.