Function Get-Transitive-Closure
(
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).