# Convex node set

From Egres Open

In a digraph *D=(V,A)* with disjoint node sets *X* and *Y*, we say that *Y* is **reachable** from *X* if there is a directed path in *D* whose first node is in *X* and last node is in *Y*.
A subset [math]T\subseteq V[/math] is called **convex** if there is no node *v* in *V-T* so that *T* is reachable
from *{v}* and *{v}* is reachable from *T*.