Locally finite approximation of Lie groups, I.
Minimal models for non-nilpotent spaces.
Moduli spaces of covers and the Hurwitz monodromy group.
Nilpotency of self homotopy equivalences with coefficients
In this paper we study the nilpotency of certain groups of self homotopy equivalences. Our main goal is to extend, to localized homotopy groups and/or homotopy groups with coefficients, the general principle of Dror and Zabrodsky by which a group of self homotopy equivalences of a finite complex which acts nilpotently on the homotopy groups is itself nilpotent.
On the connectivity of finite subset spaces
We prove that the space of nonempty subsets of cardinality at most k in a bouquet of m+1-dimensional spheres is (m+k-2)-connected. This, as shown by Tuffley, implies that the space is (m+k-2)-connected for any m-connected cell complex X.
On the finiteness of the fundamental group of a compact shrinking Ricci soliton
Myers's classical theorem says that a compact Riemannian manifold with positive Ricci curvature has finite fundamental group. Using Ambrose's compactness criterion or J. Lott's results, M. Fernández-López and E. García-Río showed that the finiteness of the fundamental group remains valid for a compact shrinking Ricci soliton. We give a self-contained proof of this fact by estimating the lengths of shortest geodesic loops in each homotopy class.
On the fundamental group of a space of sections.
On the homotopy groups of a finite dimensional space.
On the vanishing of local homotopy groups for isolated singularities of complex spaces.
Open subgroups of free topological groups
The theory of covering spaces is often used to prove the Nielsen-Schreier theorem, which states that every subgroup of a free group is free. We apply the more general theory of semicovering spaces to obtain analogous subgroup theorems for topological groups: Every open subgroup of a free Graev topological group is a free Graev topological group. An open subgroup of a free Markov topological group is a free Markov topological group if and only if it is disconnected.
Räume normierter Bilinearformen und Cliffordstrukturen.
Representation types and 2-primary homotopy groups of certain compact Lie groups.
Some analogs of Zariski's Theorem on nodal line arrangements.
Some Topological Properties of Kähler Manifolds and Homogeneous Spaces.
Suites spectrales de Serre en homotopie
Beaucoup d’informations sur les groupes de cohomologie d’un espace sont obtenues à partir de la suite spectrale de Serre. Dans cet article on construit une suite spectrale de Serre dans le cas “non stable”. Cette suite spectrale “non stable” permet des calculs de groupes d’homotopie d’espaces fonctionnels.
Tetrahedra on deformed spheres and integral group cohomology.
The braid groups of the projective plane.
The fundamental groups of subsets of closed surfaces inject into their first shape groups.
The homotopy groups of the L2-localized Mahowald spectrum.
The homotopy type of the space of degree 0 immersed plane curves.
The space Bi0 = Imm0 (S1, R2) / Diff (S1) of all immersions of rotation degree 0 in the plane modulo reparameterizations has homotopy groups π1(Bi0) = Z, π2(Bi0) = Z, and πk(Bi0) = 0 for k ≥ 3.