I is the set of nodes. F is the set of edges. N. Robertson and P.D. Seymour, Graph minors. Excluding a forest , J. Comb. A binary tree of height h a rooted tree T such that the root has degree 2, all other non leaf vertices of T have degrees 3, and every leaf of T has distance h from the root.
H contains T as a minor if and only if H contains T as a subdivision.
Excluding a forest , J. Combin. Introduction Much research has been done to compute the pathwidth of graphs. In this paper, we consider the problem to approximate the pathwidth of outerplanar graphs. The weak dual of an outerplane graph is a forest. The weak dual of a 2 connected outerplane graph is a tree.