Editing Directed acyclic graph (section)

=== Related families of graphs ===
{{multiple image
|image1=Butterfly multitree.svg|caption1=A [[multitree]], a DAG in which the subgraph reachable from any vertex induces an undirected tree (e.g. in red)
|image2=Polytree.svg|caption2=A [[polytree]], a DAG formed by orienting the edges of an undirected tree
}}
A ''[[multitree]]'' (also called a ''strongly unambiguous graph'' or a ''mangrove'') is a DAG in which there is at most one directed path between any two vertices. Equivalently, it is a DAG in which the subgraph reachable from any vertex induces an [[Tree (graph theory)|undirected tree]].<ref>{{citation
 | last1 = Furnas | first1 = George W. | author1-link = George Furnas
 | last2 = Zacks | first2 = Jeff
 | contribution = Multitrees: enriching and reusing hierarchical structure
 | doi = 10.1145/191666.191778
 | pages = 330–336
 | title = Proc. SIGCHI conference on Human Factors in Computing Systems (CHI '94)
 | year = 1994| isbn = 978-0897916509 | s2cid = 18710118 | doi-access = free}}.</ref>

A ''[[polytree]]'' (also called a ''directed tree'') is a multitree formed by orienting the edges of an undirected tree.<ref>{{citation
 | last1 = Rebane
 | first1 = George
 | last2 = Pearl
 | first2 = Judea
 | author2-link = Judea Pearl
 | contribution = The recovery of causal poly-trees from statistical data
 | pages = 222–228
 | title = Proc. 3rd Annual Conference on Uncertainty in Artificial Intelligence (UAI 1987), Seattle, WA, USA, July 1987
 | url = http://ftp.cs.ucla.edu/tech-report/198_-reports/870031.pdf
 | year = 1987
 }}.</ref>

An ''[[Arborescence (graph theory)|arborescence]]'' is a polytree formed by [[Orientation (graph theory)|orienting]] the edges of an undirected tree away from a particular vertex, called the ''root'' of the arborescence.