The -closure of a digraph is a digraph with the same vertex set as and an arc set that is the set of arcs where and are vertices of such that there is a -path in of length less than or equal to .
This Demonstration draws a directed cycle with vertices. Then it draws its -closure for a given value of . When divides , there is a set that is kernel of the -closure, and therefore is a -kernel of the original cycle. When divides , one kernel of the closure is colored in yellow.