Homotopy Groups of Spheres and Lipschitz Homotopy Groups of Heisenberg Groups

We provide a sufficient condition for the nontriviality of the Lipschitz homotopy group of the Heisenberg group, ${\pi_m^{\rm Lip}(\mathbb{H}_n)}$ , in terms of properties of the classical homotopy group of the sphere, ${\pi_m(\mathbb{S}^n)}$ . As an application we provide a new simplified proof of the fact that ${\pi_n^{\rm Lip}(\mathbb{H}_n)\neq \{0\}, n=1,2,\ldots}$ , and we prove a new result that ${\pi_{4n-1}^{\rm Lip}(\mathbb{H}_{2n})\neq \{0\}}$ for n = 1,2,… The last result is based on a new generalization of the Hopf invariant. We also prove that Lipschitz mappings are not dense in the Sobolev space ${W^{1,p}(\mathcal{M},\mathbb{H}_{2n})}$ when ${\dim \mathcal{M} \geq 4n}$ and 4n?1 ≤  p < 4n.     

Motivic Homotopy Theory

We give an informal discussion of the roots and accomplishments of motivic homotopy theory. The author gratefully acknowledges the support of the Humboldt Foundation and the ICTP, as well as the support of the NSF via the grant DMS-0457195.     

Setwise Homotopy Category

We introduce the setwise homotopy relation and prove that two chain maps induce the same cohomology map if and only if they are setwise homotopic.     

Stable Homotopy Monomorphisms

It is well known that the concept of monomorphism in a category can be defined using an appropriate pullback diagram. In the homotopy category of TOP pullbacks do not generally exist. This motivated Michael Mather to introduce another notion of homotopy pullback which does exist. The aim of this paper is to investigate the modified notion of homotopy monomorphism obtained by applying the pullback characterization using Mather's homotopy pullback. The main result of Section 1 shows that these modified homotopy monomorphisms are exactly those homotopy monomorphisms (in the usual sense) which are homotopy pullback stable, hence the terminology “stable” homotopy monomorphism. We also link these stable homotopy monomorphisms to monomorphisms and products in the track homotopy category over a fixed space. In Section 2 we answer the question: when is a (weak) fibration also a stable homotopy monomorphism? In the final section it is shown that the class of (weak) fibrations with this additional property coincides with the class of “double” (weak) fibrations. The double (weak) covering homotopy property being introduced here is a stronger version of the (W) CHP in which the final maps of the homotopies involved play the same role as the initial maps.     

Homotopy invariance of AF-embeddability

We prove that AF-embeddability is a homotopy invariant in the class of separable exact C ^*-algebras. This work was inspired by Spielberg's work on homotopy invariance of AF-embeddability and Dadarlat's serial works on AF-embeddability of residually finite dimensional C ^*-algebras. Submitted: February 2002.     

Homotopy uniqueness ofBG 2

We prove that the homotopy type ofBG ₂ is determined by its mod 2 cohomology as well as by its Weyl group data. The author is partially supported by DGICYT grant PB94-0725.     

Homotopy groups with coefficients

This paper has two goals. It is an expository paper on homotopy groups with coefficients in an abelian group and it contains new results which correct old errors and omissions in low dimensions. The homotopy groups with coefficients are functors on the homotopy category of pointed spaces. They satisfy a universal coefficient theorem, give long exact sequences when applied to fibrations, and have Hurewicz maps into homology groups with coefficients.     

Locale同伦理论

本文引入了locale连续映射同伦的概念,建立了locale同伦范畴,构造性地证明了任一locale连续映射都同伦等价于一个locale包含映射。通过引入locale H群的概念(它是locale群概念的自然推广),建立了locale同伦范畴到群同态范畴的一个反变函子。特别地,我们建立了locale同伦群范畴上的基本群函子,证明了locale L上以p为基点的基本群同构于L的谱空间pt(L)上以p为基点的基本群。因此,基本群函子是locale范畴中的一个同伦不变量。     

Homotopy coherent category theory

This article is an introduction to the categorical theory of homotopy coherence. It is based on the construction of the homotopy coherent analogues of end and coend, extending ideas of Meyer and others. The paper aims to develop homotopy coherent analogues of many of the results of elementary category theory, in particular it handles a homotopy coherent form of the Yoneda lemma and of Kan extensions. This latter area is linked with the theory of generalised derived functors.

     

Homotopy theory of bicomplexes

We define two model structures on the category of bicomplexes concentrated in the right half plane. The first model structure has weak equivalences detected by the totalisation functor. The second model structure's weak equivalences are detected by the $E^2$-term of the spectral sequence associated to the filtration of the total complex by the horizontal degree. We then extend this result to twisted complexes.     

关于同伦正则态射

该文在点标拓扑空间的范畴中引进了同伦正则态射的概念,研究了它存在的条件,性质以及它与同伦单（满）态,同伦正则单（满）态和同伦等价之间的密切关系。