Editing Planar graph (section)

===Halin graphs===
A [[Halin graph]] is a graph formed from an undirected plane tree (with no degree-two nodes) by connecting its leaves into a cycle, in the order given by the plane embedding of the tree. Equivalently, it is a [[polyhedral graph]] in which one face is adjacent to all the others. Every Halin graph is planar. Like outerplanar graphs, Halin graphs have low [[treewidth]], making many algorithmic problems on them more easily solved than in unrestricted planar graphs.<ref>{{citation
 | last1 = Sysło | first1 = Maciej M.
 | last2 = Proskurowski | first2 = Andrzej
 | contribution = On Halin graphs
 | doi = 10.1007/BFb0071635
 | pages = 248–256
 | publisher = Springer-Verlag
 | series = Lecture Notes in Mathematics
 | title = Graph Theory: Proceedings of a Conference held in Lagów, Poland, February 10–13, 1981
 | volume = 1018
 | isbn = 978-3-540-12687-4
 | year = 1983}}.</ref>