Reverse digraph

Reverse digraph --- обратный орграф.

For a given digraph [math]\displaystyle{ G }[/math], the graph [math]\displaystyle{ G_{r} = (V,E_{r}) }[/math] is said to be reversal or reverse digraph, where

[math]\displaystyle{ E_{r} = \{(x,y)| \; (y,x) \in E\}, }[/math]

or in other words,

[math]\displaystyle{ (x,y) \in E_{r} \Longleftrightarrow (y,x) \in E. }[/math]