abstract:In graph theory, a Halin graph is a planar graph constructed from a plane embedding of a tree with at least four vertices and with no vertices of degree 2, by connecting all the leaves of the tree (the vertices of degree 1) with a cycle that passes around the tree in the natural cyclic order defined by the embedding of the tree.Encyclopaedia of Mathematics, first Supplementary volume, 1988, ISBN 0-7923-4709-9, p.