The degree of a vertex of an undirected graph is the number of edges incident to the vertex:
For an undirected graph, the vertex in-degree and out-degree are equal to the vertex degree:
For a directed graph, the sum of the vertex in-degree and out-degree is the vertex degree:
Put the vertex degree, in-degree, and out-degree before, above, and below the vertex, respectively:
The sum of the degrees of all vertices of a graph is twice the number of edges:
Every graph has an even number of vertices with odd degree:
Each vertex of a

-regular graph has the same vertex degree

:
All vertices of a simple graph have a maximum degree less than the number of vertices:
A simple graph without isolated vertices has at least one pair of vertices with equal degrees: