Topics: Graph Theory


In a graph, the points that represent elements are called vertices or nodes. The set of vertices in a graph, commonly denoted by , must be non-empty.

An edge joins two vertices. Vertices have open and closed neighbourhoods.

Adjacency and Neighbours

When a vertex is joined to another vertex by means of an edge, we say that they’re adjacent and that is a neighbour of .


An isolated vertex is a vertex with degree 0.

A hanging vertex is a vertex with degree 1.