Weak dual graph

Weak dual graph --- слабо двойственный граф.

The weak dual graph of a plane graph [math]\displaystyle{ G }[/math] is the graph [math]\displaystyle{ G^{\ast} }[/math] with (finite) faces of [math]\displaystyle{ G }[/math] as its vertices, two vertices being adjacent if the corresponding faces of [math]\displaystyle{ G }[/math] share a boundary edge.