Difference digraph

Difference digraph --- разностный граф.

A digraph [math]\displaystyle{ G }[/math] is a difference digraph iff there exists an [math]\displaystyle{ S \in IN^{+} }[/math] such that [math]\displaystyle{ G }[/math] is isomorphic to the digraph [math]\displaystyle{ DD(S) = (V,A) }[/math], where [math]\displaystyle{ V = S }[/math] and [math]\displaystyle{ A = \{(i,j): i,j \in V \wedge i - j \in V\} }[/math].