Coincidence theory for set-valued maps via compactness principles

A variety of coincidence type results are presented for set-valued maps on Hausdorff topological spaces. Our theory is based on coincidence results (in fact fixed point results) for compact maps.     

Coincidence theory for multivalued maps satisfying compactness conditions on countable sets

ABSTRACT

We present a coincidence theory for set-valued maps which satisfy certain compactness-type conditions on countable sets. Our theory is based on fixed point results for compositions of set-valued self maps.     

On the homotopy type of p-completions of infra-nilmanifolds

Infra-nilmanifolds are compact K(G,1)-manifolds with G a torsion-free, finitely generated, virtually nilpotent group. Motivated by previous results of various authors on p-completions of K(G,1)-spaces with G a finite or a nilpotent group, we study the homotopy type of p-completions of infra-nilmanifolds, for any prime p. We prove that the p-completion of an infra-nilmanifold is a virtually nilpotent space which is either aspherical or has infinitely many nonzero homotopy groups. The same is true for p-localization. Moreover, we show by means of examples that rationalizations of infra-nilmanifolds may be elliptic or hyperbolic. Received: 12 December 2001 / Published online: 5 September 2002     

Constructing infra-nilmanifolds admitting an Anosov diffeomorphism

In this paper we establish an algebraic characterization of those infra-nilmanifolds modeled on a free c-step nilpotent Lie group and with an abelian holonomy group admitting an Anosov diffeomorphism. We also develop a new method for constructing examples of infra-nilmanifolds having an Anosov diffeomorphism.     

Anosov diffeomorphisms on infra-nilmanifolds associated to graphs

Anosov diffeomorphisms on closed Riemannian manifolds are a type of dynamical systems exhibiting uniform hyperbolic behavior. Therefore, their properties are intensively studied, including which spaces allow such a diffeomorphism. It is conjectured that any closed manifold admitting an Anosov diffeomorphism is homeomorphic to an infra-nilmanifold, that is, a compact quotient of a 1-connected nilpotent Lie group by a discrete group of isometries. This conjecture motivates the problem of describing which infra-nilmanifolds admit an Anosov diffeomorphism. So far, most research was focused on the restricted class of nilmanifolds, which are quotients of 1-connected nilpotent Lie groups by uniform lattices. For example, Dani and Mainkar studied this question for the nilmanifolds associated to graphs, which form the natural generalization of nilmanifolds modeled on free nilpotent Lie groups. This paper further generalizes their work to the full class of infra-nilmanifolds associated to graphs, leading to a necessary and sufficient condition depending only on the induced action of the holonomy group on the defining graph. As an application, we construct families of infra-nilmanifolds with cyclic holonomy groups admitting an Anosov diffeomorphism, starting from faithful actions of the holonomy group on simple graphs.     

Expanding maps on infra-nilmanifolds of homogeneous type

In this paper we investigate expanding maps on infra-nilmanifolds. Such manifolds are obtained as a quotient , where is a connected and simply connected nilpotent Lie group and is a torsion-free uniform discrete subgroup of , with a compact subgroup of . We show that if the Lie algebra of is homogeneous (i.e., graded and generated by elements of degree 1), then the corresponding infra-nilmanifolds admit an expanding map. This is a generalization of the result of H. Lee and K. B. Lee, who treated the 2-step nilpotent case.

     

Coincidence Wecken Property for Nilmanifolds

Let f, g: X → Y be maps from a compact infra-nilmanifold X to a compact nilmanifold Y with dim X ≥ dim Y. In this note, we show that a certain Wecken type property holds, i.e., if the Nielsen number N(f, g) vanishes then f and g are deformable to be coincidence free. We also show that if X is a connected finite complex X and the Reidemeister coincidence number R(f, g) = ∞ then f ～ f' so that C(f', g) = {x ∈ X | f'(x) = g(x)} is empty.     

准幂零流形上映射同伦类的拓扑熵的下确界

设f:M→M是准幂零流形M上的连续自映射,N∞(f)是f的渐近Nielsen数.本文应用Nielsen不动点理论,给出log N∞(f)是f的同伦类中所有映射的拓扑熵的下确界的一个充要条件,该结果是关于幂零流形上类似结果的一个本质推广.     

Coincidence Nielsen numbers for covering maps for smooth manifolds

Let be maps between closed smooth manifolds of the same dimension, and let and be finite regular covering maps. If the manifolds are nonorientable, using semi-index, we introduce two new Nielsen numbers. The first one is the Linear Nielsen number NL(f,g), which is a linear combination of the Nielsen numbers of the lifts of f and g. The second one is the Nonlinear Nielsen number NED(f,g). It is the number of certain essential classes whose inverse images by p are inessential Nielsen classes. In fact, N(f,g)=NL(f,g)+NED(f,g), where by abuse of notation, N(f,g) denotes the coincidence Nielsen number defined using semi-index.     

广义凸空间上的重合点和几乎相似重合点及其应用(英文)

We introduce the concept of a weakly G-quasiconvex map with respect to a map on generalized convex spaces and use the concept to prove coincidence point theorems and almost-like coincidence point theorems. As applications of the above results, we derive almost fixed point theorems and fixed point theorem. These main results generalize and improve some known results in the literature.     

Coincidence Points and Invariant Approximation Results for Multimaps

Some coincidence point theorems satisfying a general contractive condition are proved. As applications, some invariant approximation results are also obtained and several related results in the literature are either extended or improved.     

Coincidence and fixed points for hybrid strict contractions

We define the property (E.A) for single-valued and multivalued mappings and introduce the notion of T-weak commutativity for a hybrid pair (f,T) of single-valued and multivalued maps. We obtain some coincidence and fixed point theorems for this class of maps and derive, as application, an approximation theorem.     

Coincidence and fixed points for maps on topological spaces

The existence of coincidence and fixed points for continuous mappings on pseudo-compact completely regular topological spaces are proved. Our results are different from known, or are generalizations, extensions and improvements of the corresponding results due to Jungck, Liu and Liu et al. Further, the Edelstein result for contractive mappings is extended to Hausdorff (not necessarily completely regular) topological spaces and generalized in many aspects. An example is presented to show that our results are genuine generalizations of the Edelstein result.     

Coincidence set of minimal surfaces for the thin obstacle

We consider the Thin Obstacle Problem for minimal surfaces in two dimensions. The coincidence set for an analytic obstacle is proved to be a finite union of intervals. We show also that the topological structure of the coincidence set is generically identical to the above in the space of twice-continuously differentiable obstacles.