Topological complexity, fibrations and symmetry

We show how locally smooth actions of compact Lie groups on a manifold X can be used to obtain new upper bounds for the topological complexity TC(X), in the sense of Farber. We also obtain new bounds for the topological complexity of finitely generated torsion-free nilpotent groups.     

A lower bound for higher topological complexity of real projective space

We obtain an explicit formula for the best lower bound for the higher topological complexity, ${\mathrm{TC}}_k(R{P}^n)$, of real projective space implied by mod 2 cohomology.     

Ganea and Whitehead definitions for the tangential Lusternik-Schnirelmann category of foliations

This work solves the problem of elaborating Ganea and Whitehead definitions for the tangential category of a foliated manifold. We develop these two notions in the category S-Top of stratified spaces, that are topological spaces X endowed with a partition F and compare them to a third invariant defined by using open sets. More precisely, these definitions apply to an element (X,F) of S-Top together with a class A of subsets of X; they are similar to invariants introduced by M. Clapp and D. Puppe.If (X,F)∈S-Top, we define a transverse subset as a subspace A of X such that the intersection S∩A is at most countable for any S∈F. Then we define the Whitehead and Ganea LS-categories of the stratified space by taking the infimum along the transverse subsets. When we have a closed manifold, endowed with a C¹-foliation, the three previous definitions, with A the class of transverse subsets, coincide with the tangential category and are homotopical invariants.     

Lower bounds¶for the relative Lusternik–Schnirelmann category

We give estimates of numerical homotopy invariants of the pair (X,X×S ^p ) in terms of homotopy invariants of X. More precisely, we prove that σ ^{p +1} cat(X) + 1 ≤ cat(X,X×S ^p }), that and that e(X,X×S< ^p )=e(X)+1, where σ ^{p +1} cat is the (relative) σ category of Vandembroucq and e is the (relative) Toomer invariant. The proof is based on an extension of Milnor's construction of the classifying space of a topological group to a relative setting (due to Dold and Lashof). Received: 14 October 1998 / Revised version: 5 November 1999     

The Lyusternik-Shnirel’man category, vector bundles, and immersions of manifolds

One of our two main results exhibits for a vector bundle over a compact Hausdorff spaceX an interplay between its span, its possible splittings, and the Lyusternik-Shnirel’man category ofX. The other main result, also on vector bundles and the Lyusternik-Shnirel’man category, enables us to derive certain inequalities connecting the immersion codimension, the stable span, and the Lyusternik-Shnirel’man category of a smooth closed manifold which is not stably parallelizable. Our results are applicable in various situations of general interest.     

On higher analogs of topological complexity

Farber introduced a notion of topological complexity TC(X) that is related to robotics. Here we introduce a series of numerical invariants TCn(X), n=2,3,… , such that TC₂(X)=TC(X) and TCn(X)?TCn+1(X). For these higher complexities, we define their symmetric versions that can also be regarded as higher analogs of the symmetric topological complexity.     

Symplectic matrices with predetermined left eigenvalues

We prove that given four arbitrary quaternion numbers of norm 1 there always exists a 2×2 symplectic matrix for which those numbers are left eigenvalues. The proof is constructive. An application to the LS category of Lie groups is given.     

Lusternik-Schnirelmann category of a sphere-bundle over a sphere

We determine the Lusternik-Schnirelmann (L-S) category of a total space of a sphere-bundle over a sphere in terms of primary homotopy invariants of its characteristic map, and thus providing a complete answer to Ganea's Problem 4. As a result, we obtain a necessary and sufficient condition for a total space N to have the same L-S category as its ‘once punctured submanifold’ N\{P},P∈N. Also, necessary and sufficient conditions for a total space M to satisfy Ganea's conjecture are described.     

A theory of PWD-structures

A general study is undertaken of product-wedge-diagonal (=PWD) structures on a space. In part this concept may be viewed as arising from G.W. Whitehead's fat-wedge characterization of Lusternik-Schnirelmann category. From another viewpoint PWD-structures occupy a distinguished position among those structures that provide data allowing Hopf invariants to be defined. Indeed the Hopf invariant associated with a PWD-structure is a crucial component of the structure. Our overall theme addresses the basic question of existence of compatible structures on X and Y with regard to a map X→Y. A principal result of the paper uses Hopf invariants to formulate a Berstein-Hilton type result when the space involved is a double mapping cylinder (or homotopy pushout). A decomposition formula for the Hopf invariant (extending previous work of Marcum) is provided in case the space is a topological join U*V that has PWD-structure defined canonically via the join structure in terms of diagonal maps on U and V.     

The Topological Tverberg Theorem and winding numbers

The Topological Tverberg Theorem claims that any continuous map of a (q-1)(d+1)-simplex to R^d identifies points from q disjoint faces. (This has been proved for affine maps, for d?1, and if q is a prime power, but not yet in general.)The Topological Tverberg Theorem can be restricted to maps of the d-skeleton of the simplex. We further show that it is equivalent to a “Winding Number Conjecture” that concerns only maps of the (d-1)-skeleton of a (q-1)(d+1)-simplex to R^d. “Many Tverberg partitions” arise if and only if there are “many q-winding partitions.”The d=2 case of the Winding Number Conjecture is a problem about drawings of the complete graphs K_3q-2 in the plane. We investigate graphs that are minimal with respect to the winding number condition.     

The fibrewise Leray–Schauder index

The index constructed by Leray and Schauder in 1934 admits generalizations in two directions to infinite-dimensional fixed-point and vector field indices. We present the constructions of fibrewise equivariant indices of both types and illustrate the definitions by applications to the stable homo-topy Fuller index and Seiberg–Witten invariant. Dedicated to the memory of Jean Leray     

Proper L-S category, fundamental pro-groups and 2-dimensional proper co-H-spaces

This paper presents a study of one-ended locally finite CW-complexes with proper L-S category ?2. We detect the class of towers of groups which can be the fundamental pro-group of a space of proper L-S category 2. A second part of the paper is concerned with two-dimensional CW-complexes. For these, we give different characterizations of spaces with proper L-S category ?2.     

An inductive Lusternik-Schnirelmann category in a model category

We prove that the notion of an inductive category in a model category agrees with the Ganea approach given by Doeraene. This notion also coincides with the topological one when we consider the category of (well-)pointed topological spaces. An application is given.     

The Lyusternik–Shnirel'man category,¶vector bundles, and immersions of manifolds

One of our two main results exhibits for a vector bundle over a compact Hausdorff space X an interplay between its span, its possible splittings, and the Lyusternik–Shnirel'man category of X. The other main result, also on vector bundles and the Lyusternik–Shnirel'man category, enables us to derive certain inequalities connecting the immersion codimension, the stable span, and the Lyusternik–Shnirel'man category of a smooth closed manifold which is not stably parallelizable. Our results are applicable in various situations of general interest. Received: 4 September 1997     

Fixed point sets of fiber-preserving maps

Let be a fiber bundle where E, B and Y are connected finite polyhedra. Let be a fiber-preserving map and a closed, locally contractible subset. We present necessary and sufficient conditions for A and its subsets to be the fixed point sets of maps fiber homotopic to f. The necessary conditions correspond to those introduced by Schirmer in 1990 but, in the fiber-preserving setting, homotopies are fiberpreserving. Those conditions are shown to be sufficient in the presence of additional hypotheses on the bundle and on the map f. The hypotheses can be weakened in the case that f is fiber homotopic to the identity.     

The evaluation subgroup of a fibre inclusion

Let be a fibration of simply connected CW complexes of finite type with classifying map . We study the evaluation subgroup Gn(E,X;j) of the fibre inclusion as an invariant of the fibre-homotopy type of ξ. For spherical fibrations, we show the evaluation subgroup may be expressed as an extension of the Gottlieb group of the fibre sphere provided the classifying map h induces the trivial map on homotopy groups. We extend this result after rationalization: We show that the decomposition G_∗(E,X;j)⊗Q=(G_∗(X)⊗Q)⊕(π_∗(B)⊗Q) is equivalent to the condition Q(h_?)=0.     

Functors on the category of quasi-fibrations

We consider the following questions: when can we extend a continuous endofunctor on Top the category of topological spaces to a fibrewise continuous endofunctor on Top(2) the category of continuous maps? If this is true, does such fibrewise continuous endofunctor preserve fibrations? In this paper, we define Fib the topological category of cell-wise trivial fibre spaces over polyhedra and show that any continuous endofunctor on Top induces a fibrewise continuous endofunctor on Fib preserving the class of quasi-fibrations.