Function Get-Transitive-Closure

Part of:

package cl-graph
( get-transitive-closure < vertex-list > &optional < depth > )

Given a list of vertices, returns a combined list of all of the nodes
in the transitive closure(s) of each of the vertices in the list
(without duplicates). Optional DEPTH limits the depth (in both the
child and parent directions) to which the closure is gathered; default
nil gathers the entire closure(s).