PyPedal includes tools for working with pedigrees as algebraic structures known as directed graphs, or digraphs. Digraphs are not graphs in the sense of graphics for presentation or display. Rather, they are mathematical abstractions, the study of which can provide interesting information about the structure of a population. A digraph represents a pedigree as a set of vertices (also called nodes), which correspond to animals, and a collection of edges, which connect nodes to one another. In the context of a pedigree, edges indicate that a parent-offspring relationship exists between two animals. If a path can be constructed between two vertices (animals) in the graph then those animals are related. If no path can be constructed between teo nodes, then no relatinship exists between the two. Routines for working with graphs (also called networwks) are contained in the pyp_network module ()