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Graph minors. III. Planar tree-width. (English) Zbl 0548.05025
[For part I see ibid. 35, 39-61 (1983; Zbl 0521.05062.]
This paper continues the important work by the authors on graph minors. A graph H is a minor of a graph G if H can be obtained from a subgraph of G by contraction. The tree decomposition of a graph G is a pair (T,X) where T is a tree and X is a family of subsets of V(G): $$X=\{X_ t:\quad t\in V(T)\}$$ such that (i) the union of the $$X_ t$$ is V(G); (ii) for every edge e of G, there exists an $$X_ t$$ containing both ends of e; and (iii) for t, t’, t”$$\in V(T)$$, if t’ is on the path of T between t and t”, then $$X_ t\cap X_{t''}\subseteq X_{t'}.$$ The width of the tree decomposition is the maximum of $$| X_ t| -1.$$ The graph G has tree-width w if w is the minimum width of any tree decomposition of G. The author’s main result is: For every planar graph H, there is a number w such that every planar graph with no minor isomorphic to H has tree- width $$\leq w$$.
Reviewer: A.Tucker

##### MSC:
 05C05 Trees 05C99 Graph theory
##### Keywords:
planar graph; tree-width; graph minors; tree decomposition
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##### References:
 [1] Robertson, N; Seymour, P.D, Graph minors. I. excluding a forest, J. combin. theory ser. B, 35, 39-61, (1983) · Zbl 0521.05062 [2] {\scN. Robertson and P. D. Seymour}, Graph minors. II. Algorithmic aspects of tree-width, submitted. · Zbl 0611.05017 [3] {\scN. Robertson and P. D. Seymour}, Graph minors. IV. Tree-width and well-quasiordering, submitted. · Zbl 0719.05032 [4] {\scN. Robertson and P. D. Seymour}, Graph minors. V. Excluding a planar graph, submitted. · Zbl 1023.05040 [5] {\scN. Robertson and P. D. Seymour}, Graph minors. VI. Disjoint paths on a surface, in preparation. · Zbl 0658.05044 [6] {\scN. Robertson and P. D. Seymour}, Graph minors. VII. Disjoint paths on a surface, in preparation. · Zbl 0658.05044
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