### Set

 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 $u\in\phi(v)\implies v\in\phi(u)$

### Discussion

The value $\phi(v)$ denotes the set of vertices which are connected to $v$.

The adjacency lists describe simple graph.