We introduce a notion of bipartite minors and prove a bipartite analog of Wagner’s theorem: a bipartite graph is planar if and only if it does not contain K3,3 as a bipartite minor. Similarly, we provide a forbidden minor characterization for outerplanar graphs and forests. We then establish a recursive characterization of bipartite (2, 2)-Laman graphs — a certain family of graphs that contains...

We study the maximal number of triangulations that a planar set of n points can have, and show that it is at most 30n. This new bound is achieved by a careful optimization of the charging scheme of Sharir and Welzl (2006), which has led to previous best upper bound of 43n for the problem. Moreover, this new bound is useful for bounding the number of other types of planar (i.e., crossing free) s...

Yannakakis and Gavril showed in [10] that the problem of finding a maximal matching of minimum size (MMM for short), also called Minimum Edge Dominating Set, is NP-hard in bipartite graphs of maximum degree 3 or planar graphs of maximum degree 3. Horton and Kilakos extended this result to planar bipartite graphs and planar cubic graphs [6]. Here, we extend the result of Yannakakis and Gavril in...

We give here three simple linear time algorithms on planar graphs: a 4-connexity test for maximal planar graphs, an algorithm enumerating the triangles and a 3-connexity test. Although all these problems got already linear-time solutions, the presented algorithms are both simple and efficient. They are based on some new theoretical results. Communicated by T. Nishizeki, R. Tamassia and D. Wagne...

In this paper, we consider the weakened Hilbert’s 16th problem for symmetric planar perturbed polynomial Hamiltonian systems. In particular, a perturbed Hamiltonian polynomial vector field of degree 9 is studied, and an example of Z10-equivariant planar perturbed Hamiltonian systems is constructed. With maximal number of closed orbits, it gives rise to different configurations of limit cycles. ...

We will show that shellability, Cohen-Macaulayness and vertexde composability of a graded, planar poset P are all equivalent with the fact that P has the maximal possible number of edges. Also, for a such poset we will find an R−labelling with {1, 2} as the set of labels. Using this, we will obtain all essential linear inequalities for the flag h−vectors of shellable planar posets from [1]. AMS...

| We explore the question of counting, and estimating the number and the fraction of, in-scribable graphs. In particular we will concern ourselves with the number of inscribable and circum-scribable maximal planar graphs (synonym: simplicial polyhedra) on V vertices, or, dually, the number of circumscribable and inscribable trivalent (synonyms: 3-regular, simple) polyhedra. For small V we provi...

We give a simple upper bound on k for k-path-hamiltonianness of a graph. Also given are exact values for maximal planar graphs. UN/VERSJTY LIBRARIES CARNEGIE-MELLON UNIVERSITY PITTSBURGH, PENNSYLVANIA 15213

Different formulas counting families of non isomorphic chord diagrams are given : planar and toroidal ones and those of maximal genus. These formulas are obtained establishing results on the structure of the automorphism group of diagrams of a given genus.

A planar 3-connected graph G is essentially 4-connected if for any 3-separator S of G, one component of the graph obtained from G by removing S is a single vertex. B. Jackson and N.C. Wormald proved that an essentially 4-connected planar graph on n vertices contains a cycle C such that |V (C)| ≥ 2n+4 5 . For a cubic essentially 4-connected planar graph G, B. Grünbaum, J. Malkevitch , and C.-Q. ...