TL;DR: Even polyhedral decompositions of a trivalent graph have been shown to have a Tait colouring by three colours a, b, c as mentioned in this paper, which is a strong conjecture.
Abstract: A polyhedral decomposition of a finite trivalent graph G is defined as a set of circuits = {C1, C2, … Cm} with the property that every edge of G occurs exactly twice as an edge of some Ck. The decomposition is called even if every Ck is a simple circuit of even length. If G has a Tait colouring by three colours a, b, c then the (a, b), (b, c) and (c, a) circuits obviously form an even polyhedral decomposition. It is shown that the converse is also true: if G has an even polyhedral decomposition then it also has a Tait colouring. This permits an equivalent formulation of the four colour conjecture (and a much stronger conjecture of Branko Grunbaum) in terms of polyhedral decompositions alone.
TL;DR: A linear time algorithm for the Steiner problem in Halin networks is presented, providing another example where the recursive structure of the underlying network leads to an efficient algorithm.
TL;DR: It is proved that the incidence coloring number for Halin graphs and outerplanar graphs of maximum degree greater than or equal to 4 is equal to the maximum degree of the graph plus 1.
TL;DR: It is proved that such a graph on n vertices contains cycles of all lengths l, 3 ≤ ln, except, possibly, for one even value m of l.
Abstract: A Halin graph is a plane graph H = T U C, where T is a plane tree with no vertex of degree two and at least one vertex of degree three or more, and C is a cycle connecting the endvertices of T in the cyclic order determined by the embedding of T. We prove that such a graph on n vertices contains cycles of all lengths l, 3 ≤ ln, except, possibly, for one even value m of l. We prove also that if the tree T contains no vertex of degree three then G is pancyclic.
TL;DR: The strong chromatic index of a graph G, denoted by [email protected]^'(G), is the minimum number of colors needed for a strong edge coloring of G.