  Bidirected graphs generalize directed and undirected graphs in that edges are
oriented locally at every node. The natural notion of the degree of a node that
takes into account (local) orientations is that of net-degree. In this paper,
we extend the following four topics from (un)directed graphs to bidirected
graphs:
  - Erd\H{o}s-Gallai-type results: characterization of net-degree sequences,
  - Havel-Hakimi-type results: complete sets of degree-preserving operations,
  - Extremal degree sequences: characterization of uniquely realizable
sequences, and
  - Enumerative aspects: counting formulas for net-degree sequences.
  To underline the similarities and differences to their (un)directed
counterparts, we briefly survey the undirected setting and we give a thorough
account for digraphs with an emphasis on the discrete geometry of degree
sequences. In particular, we determine the tight and uniquely realizable degree
sequences for directed graphs.
