(no text body provided yet)

- Definition: Digraph, Initial and Terminal Vertices, Loops, Parallel and Inverse Edges, Simple Digraph
- Definition: Incidence, Adjacency, Predecessor and Successor Vertices, Neighbours
- Definition: Subdigraphs and Superdigraphs; Induced Subdigraph
- Definition: Vertex Degrees for Digraphs
- Lemma: Handshaking Lemma for Finite Digraphs