Semikernel modulo F

Semikernel modulo [math]\displaystyle{ F }[/math] --- полуядро по модулю [math]\displaystyle{ F }[/math].

Let [math]\displaystyle{ F }[/math] be a set of arcs of a digraph [math]\displaystyle{ D }[/math] (i.e., [math]\displaystyle{ F \subseteq A(D) }[/math]), a set [math]\displaystyle{ S \subseteq V(D) }[/math] is called a semikernel of [math]\displaystyle{ D }[/math] modulo [math]\displaystyle{ F }[/math], if [math]\displaystyle{ S }[/math] is an independent set of vertices such that for every [math]\displaystyle{ z \in V(D) \setminus S }[/math] for which there exists an [math]\displaystyle{ Sz }[/math]-arc of [math]\displaystyle{ D \setminus F }[/math] there also exists a [math]\displaystyle{ zS }[/math]-arc in [math]\displaystyle{ D }[/math].