arXiv subjects
Publications and source records attributed to Robert Cauty.
We prove the following generalisation of Schauder's fixed point conjecture: Let $C_1,...,C_n$ be convex subsets of a Hausdorff topological vector space. Suppose that the $C_i$ are closed in $C=C_1\cup...\cup C_n$. If $f:C\to C$ is a continuous function whose image is contained in a compact subset of $C$, then its Lefschetz number $Λ(f)$ is defined. If $Λ(f)\ne0$, then $f$ has a fixed point.
A topological space is locally equiconnected if there exists a neighborhood $U$ of the diagonal in $X\times X$ and a continuous map $λ:U\times[0,1]\to X$ such that $λ(x,y,0)=x$, $λ(x,y,1)=y$ et $λ(x,x,t)=x$ for $(x,y)\in U$ and $(x,t)\in X\times[0,1]$. This class contains all ANRs, all locally contractible topological groups and the open subsets of convex subsets of linear topological spaces. In a series of papers, we extended the fixed point theory of compact continuous maps, which was well developped for ANRs, to all separeted locally equiconnected spaces. This generalization includes a proof of Schauder's conjecture for compact maps of convex sets. This paper is a survey of that work. The generalization has two steps: the metrizable case, and the passage from the metrizable case to the general case. The metrizable case is, by far, the most difficult. To treat this case, we introduced in [4] the notion of algebraic ANR. Since the proof that metrizable locally equiconnected spaces are algebraic ANRs is rather difficult, we give here a detaled sketch of it in the case of a compact convex subset of a metrizable t.v.s.. The passage from the metrizable case to the general case uses a free functor and representations of compact spaces as inverse limits of some special inverse systems of metrizable compacta.
We prove that each non-separable completely metrizable convex subset of a Frechet space is homeomorphic to a Hilbert space. This resolves an old (more than 30 years) problem of infinite-dimensional topology. Combined with the topological classification of separable convex sets due to Klee, Dobrowoslki and Torunczyk, this result implies that each closed convex subset of a Frechet space is homemorphic to $[0,1]^n\times [0,1)^m\times l_2(k)$ for some cardinals $0\le n\leω$, $0\le m\le 1$ and $k\ge 0$.
We survey some properties of homotopical and homological $Z_n$-sets in topological spaces.