Exhausting curve complexes by finite rigid sets on nonorientable surfaces

Let [Formula: see text] be a compact, connected, nonorientable surface of genus [Formula: see text] with [Formula: see text] boundary components. Let [Formula: see text] be the curve complex of [Formula: see text]. We prove that if [Formula: see text] or [Formula: see text], then there is an exhaustion of [Formula: see text] by a sequence of finite rigid sets. This improves the author’s result on exhaustion of [Formula: see text] by a sequence of finite superrigid sets.

On the topological complexity of manifolds with abelian fundamental group

We find conditions which ensure that the topological complexity of a closed manifold M with abelian fundamental group is nonmaximal, and see through examples that our conditions are sharp. This generalizes results of Costa and Farber on the topological complexity of spaces with small fundamental group. Relaxing the commutativity condition on the fundamental group, we also generalize results of Dranishnikov on the Lusternik–Schnirelmann category of the cofibre of the diagonal map Δ : M → M × M {\Delta:M\to M\times M} for nonorientable surfaces by establishing the nonmaximality of this invariant for a large class of manifolds.

About Structure of Graph Obstructions for Klein Surface with 9 Vertices

The structure of the 9 vertex obstructive graphs for the nonorientable surface of the genus 2 is established by the method of j-transformations of the graphs. The problem of establishing the structural properties of 9 vertex obstruction graphs for the surface of the undirected genus 2 by the method of j-transformation of graphs is considered. The article has an introduction and 5 sections. The introduction contains the main definitions, which are illustrated, to some extent, in Section 1, which provides several statements about their properties. Sections 2 – 4 investigate the structural properties of 9 vertex obstruction graphs for an undirected surface by presenting as a j-image of several graphs homeomorphic to one of the Kuratovsky graphs and at least one planar or projective-planar graph. Section 5 contains a new version of the proof of the statement about the peculiarities of the minimal embeddings of finite graphs in nonorientable surfaces, namely, that, in contrast to oriented surfaces, cell boundaries do not contain repeated edges. Also in section 5 the other properties peculiar to embeddings of graphs to non-oriented surfaces and the main result are given. The main result is Theorem 1. Each obstruction graph H for a non-oriented surface N2 of genus 2 satisfies the following. 1. An arbitrary edge u,u = (a,b) is placed on the Mebius strip by some minimal embedding of the graph H in N3 and there exists a locally projective-planar subgraph K of the graph H \ u which satisfies the condition: (tK({a,b},N3)=1)˄(tK\u({a,b},N2)=2), where tK({a,b},N) is the number of reachability of the set {a,b} on the nonorientable surface N; 2. There exists the smallest inclusion of many different subgraphs Ki of a 2-connected graph H homeomorphic to the graph K+e, where K is a locally planar subgraph of the graph H (at least K+e is homemorphic to K5 or K3,3), which covers the set of edges of the graph H. Keywords: graph, Klein surface, graph structure, graph obstruction, non-oriented surface, Möbius strip.

On the EIT problem for nonorientable surfaces

Let {(\Omega,g)} be a smooth compact two-dimensional Riemannian manifold with boundary and let {\Lambda_{g}:f\mapsto\partial_{\nu}u|_{\partial\Omega}} be its DN map, where u obeys {\Delta_{g}u=0} in Ω and {u|_{\partial\Omega}=f}. The Electric Impedance Tomography Problem is to determine Ω from {\Lambda_{g}}. A criterion is proposed that enables one to detect (via {\Lambda_{g}}) whether Ω is orientable or not. The algebraic version of the BC-method is applied to solve the EIT problem for the Moebius band. The main instrument is the algebra of holomorphic functions on the double covering {{\mathbb{M}}} of M, which is determined by {\Lambda_{g}} up to an isometric isomorphism. Its Gelfand spectrum (the set of characters) plays the role of the material for constructing a relevant copy {(M^{\prime},g^{\prime})} of {(M,g)}. This copy is conformally equivalent to the original, provides {\partial M^{\prime}=\partial M}, {\Lambda_{g^{\prime}}=\Lambda_{g}}, and thus solves the problem.

McShane-Type Identities for Quasifuchsian Representations of Nonorientable Surfaces

We show that Norbury’s McShane identity for nonorientable cusped hyperbolic surfaces $N$ generalizes to quasifuchsian representations of $\pi _1(N)$ as well as pseudo-Anosov mapping Klein bottles with singular fibers given by $N$.

The Birman-Hilden property of covering spaces of nonorientable surfaces

UDC 517.5 Let p : N ˜ → N be a finite covering space of nonorientable surfaces, where χ ( N ˜ ) < 0 . We search whether or notphasthe Birman – Hilden property.