| context | $V$ … countable set |
| definiendum | $ \phi\in\mathrm{it} $ |
| postulate | $ \mathrm{dom}\ \phi = V $ |
| for all | $ v,u\in V $ |
| postulate | $ \phi(v)\subseteq V $ |
| postulate | $ u\in\phi(v)\implies v\in\phi(u) $ |
The value $\phi(v)$ denotes the set of vertices which are connected to $v$.
The adjacency lists describe simple graph.