Join of graphs

Join of graphs --- соединение графов.

The join of the graphs [math]\displaystyle{ G }[/math] and [math]\displaystyle{ H }[/math] is the graph with a vertex set [math]\displaystyle{ V(G) \cup V(H) }[/math] and edge set [math]\displaystyle{ E(G) \cup E(H) \cup \{(u,v): u \in V(G), v \in V(H)\} }[/math].

The join of digraphs [math]\displaystyle{ D_{1} }[/math] and [math]\displaystyle{ D_{2} }[/math] consists of [math]\displaystyle{ D_{1} \cup D_{2} }[/math] together with all bidirectional arcs between any vertex of [math]\displaystyle{ D_{1} }[/math] and any vertex of [math]\displaystyle{ D_{2} }[/math].