From this graph theory lesson :
A graph is a non-empty finite set $V$ of elements called vertices together with a possibly empty set $E$ of pairs of vertices called edges. Here are a few examples of graphs:
- Vertex set $V = \{a, b, c, d\}$ and edge set $E = \{(a, b), (b, d)\}$
- Vertex set $V = \{1, 2, 3, 4\}$ and edge set $E = \{(2, 4)\}$
- Vertex set $V = \{wolf, goat, cabbage\}$ and edge set $E = \{(wolf, cabbage)\}$
- Vertex set $V = \{A, B, C\}$ and edge set $E = \emptyset$.
Is this the correct definition for graphs ? If the graph has possibly empty empty edges how can it be represented diagramatically ? What can be a practical example of a graph where there are no edges at all ?