Graph

A graph $G:=(V,E)$ is defined by two sets $V$ and $E\subset V\times V$.
The elements of $V$ are called vertices while the elements of $E$ are called edges of the graph.

Examples

• The graph $G=(\{1,2,3,4,6\}, \{(1,1), (2,3), (3,4), (4,2)\})$ can be represented by an isolated vertex $1$ linked to itself (called loop), a triangle made of vertices $2,3,4$ and another isolated vertex called $6$.