It is well known that ω-limit sets are internally chain transitive and have weak incompressibility; the converse is not generally true, in either case. However, it has been shown that a set is weakly incompressible if and only if it is an abstract ω-limit set, and separately that in shifts of finite type, a set is internally chain transitive if and only if it is a (regular) ω-limit set. In this paper we generalise these and other results, proving that the characterization for shifts of finite type holds in a variety of topologically hyperbolic systems (defined in terms of expansive and shadowing properties), and also show that the notions of internal chain transitivity and weak incompressibility coincide in compact metric spaces.2000 Mathematics Subject Classification. 37B25, 37B45, 37E05, 54F15, 54H20.

The main result of this paper is that a map f : X → X which has shadowing and for which the space of ω-limits sets is closed in the Hausdorff topology has the property that a set A ⊆ X is an ω-limit set if and only if it is closed and internally chain transitive. Moreover, a map which has the property that every closed internally chain transitive set is an ω-limit set must also have the property that the space of ω-limit sets is closed. As consequences of this result, we show that interval maps with shadowing have the property that every internally chain transitive set is an ω-limit set of a point, and we also show that topologically hyperbolic maps and certain quadratic Julia sets have a closed space of ω-limit sets 2000 Mathematics Subject Classification. 37B50, 37B10, 37B20, 54H20.

A set Λ is internally chain transitive if for any x,y∈Λ and ϵ>0 there is an ϵ-pseudo-orbit in Λ between x and y. In this paper we characterize all ω-limit sets in shifts of finite type by showing that, if Λ is a closed, strongly shift-invariant subset of a shift of finite type, X, then there is a point z∈X with ω(z)=Λ if and only if Λ is internally chain transitive. It follows immediately that any closed, strongly shift-invariant, internally chain transitive subset of a shift space over some alphabet ℬ is the ω-limit set of some point in the full shift space over ℬ. We use similar techniques to prove that, for a tent map f, a closed, strongly f-invariant, internally chain transitive subset of the interval is the ω-limit set of a point provided it does not contain the image of the critical point. We give an example of a sofic shift space Z𝒢 (a factor of a shift space of finite type) that is not of finite type that has an internally chain transitive subset that is not the ω-limit set of any point in Z𝒢.

No abstract

Abstract. The topology of one-dimensional invariant sets (attractors) is of great interest. R. F. Williams [20] demonstrated that hyperbolic one-dimensional non-wandering sets can be represented as inverse limits of graphs with bonding maps that satisfy certain strong dynamical properties. These spaces have "homogeneous neighborhoods" in the sense that small open sets are homeomorphic to the product of a Cantor set and an arc. In this paper we examine inverse limits of graphs with more complicated bonding maps. This allows us to understand the topology of a wider class of spaces that includes both hyperbolic and non-hyperbolic attractors. Many of these spaces have the property that most small open sets are homeomorphic to the product of a Cantor set and an arc. The interesting "inhomogeneities" occur away from these neighborhoods. By examining the dynamics of the bonding maps that generate these spaces, we characterize the inhomogeneities, and we show that there is a natural nested hierarchy in the collection of these points that is topological.1. Introduction. The topology of hyperbolic one-dimensional sets left invariant under a dynamical system is well understood. R. F. Williams [20] showed that these can be described as inverse limits of branched onemanifolds, and he developed much of the necessary theory for analyzing these spaces ([21], [22]). Anderson and Putnam [1] have shown that this class of spaces also includes the substitution tiling spaces. Recently, Barge and Diamond classified all such spaces that are orientable [3]. Topological invariants for the non-orientable case have also been found (see [23]).However, very little is understood about the topology of one-dimensional invariant sets that are not hyperbolic. Perhaps the main difficulty in understanding the structure of these spaces is the fact that they tend to be quite complicated locally. Hyperbolic one-dimensional sets are solenoid-like in the sense that all sufficiently small neighborhoods are homeomorphic to the product of a Cantor set and an arc. Without the restriction that the space is hyperbolic, small neighborhoods can display very complicated structure.