Every k-tree has book thickness at most k + 1, and this bound is best possible for all k ≥ 3. Vandenbussche et al. (2009) proved that every k-tree that has a smooth degree-3 tree decomposition with width k has book thickness at most k. We prove this result is best possible for k ≥ 4, by constructing a k-tree with book thickness k + 1 that has a smooth degree-4 tree decomposition with width k. This solves an open problem of Vandenbussche et al. ( 2009)
IntroductionConsider a drawing of a graph 1 G in which the vertices are represented by distinct points on a circle in the plane, and each edge is a chord of the circle between the corresponding points. Suppose that each edge is assigned one of k colours such that crossing edges receive distinct colours. This structure is called a k-page book embedding of G: one can also think of the vertices as being ordered along the spine of a book, and the edges that receive the same colour being drawn on a single page of the book without crossings. The book thickness of G, denoted by bt(G), is the minimum integer k for which there is a k-page book embedding of G. Book embeddings, first defined by Ollmann [9], are ubiquitous structures with a variety of applications; see [5] for a survey with over 50 references. A book embedding is also called a stack layout, and book thickness is also called stacknumber, pagenumber and fixed outerthickness.This paper focuses on the book thickness of k-trees.or G has a k-simplicial vertex v and G \ v is a k-tree. In the latter case, we say that G is obtained from G − v by adding v onto the k-clique N G (v).