In a simple graph, the degree of a vertex is the number of neighbors of the vertex. In a digraph, we define the degree of a vertex to be the number of elements in the unique union of the parents and children of the vertex.

i1 : D = digraph({1,2,3,4},{{1,2},{2,3},{3,4},{4,2},{2,4}}); |

i2 : degree(D, 3) o2 = 2 |

i3 : degree(D, 2) o3 = 3 |