Certain results on extending maps taking values in Hilbert manifolds by maps which are close to being embeddings are presented. Sufficient conditions on a map under which it is extendable by an embedding are given. In particular, it is shown that if X is a completely metrizable space of topological weight not greater than α ≥ ℵ₀, A is a closed set in X and f: X → M is a map into a manifold M modelled on a Hilbert space of dimension α such that $f\left(X\setminus A\right)\cap \overline{f\left(\partial A\right)}=\varnothing$, then for every open cover of M there is a map g:...

The Dehn quandle, Q, of a surface was defined via the action of Dehn twists about circles on the surface upon other circles. On the torus, 𝕋², we generalize this to show the existence of a quandle Q̂ extending Q and whose elements are measured geodesic foliations. The quandle action in Q̂ is given by applying a shear along such a foliation to another foliation. We extend some results which related Dehn quandle homology to the monodromy of Lefschetz fibrations. We apply certain quandle 2-cycles...

Complexes of groups $G\left(X\right)$ over ordered simplicial complexes $X$ are generalizations to higher dimensions of graphs of groups. We first relate them to complexes of spaces by considering their classifying space $BG\left(X\right)$. Then we develop their homological algebra aspects. We define the notions of homology and cohomology of a complex of groups $G\left(X\right)$ with coefficients in a $G\left(X\right)$-module and show the existence of free resolutions. We apply those notions to study extensions of complexes of groups with constant or abelian kernel....

We characterize, in terms of X, the extensional dimension of the Stone-Čech corona βX∖X of a locally compact and Lindelöf space X. The non-Lindelöf case is also settled in terms of extending proper maps with values in $I^{\tau }\setminus L$, where L is a finite complex. Further, for a finite complex L, an uncountable cardinal τ and a $Z_{\tau }$-set X in the Tikhonov cube $I^{\tau }$ we find a necessary and sufficient condition, in terms of $I^{\tau }\setminus X$, for X to be in the class AE([L]). We also introduce a concept of a proper absolute extensor and...

The archetype for the questions considered is: “Which plane oriented curves in the plane are representable as the images of the boundary of a disk under holomorphic function?” This question is equivalent to: “Which immersion of the circle in the plane are extendable to smooth sense preserving (= non-negative jacobian) mappings of the closed disk with the jacobian positive on the boundary?”The second question is generalized in terms of the genus and dimension of the source and target. An exposition...

Let $𝒟$ denote a true dimension function, i.e., a dimension function such that $𝒟\left({ℝ}^n\right)=n$ for all $n$. For a space $X$, we denote the hyperspace consisting of all compact connected, non-empty subsets by $C\left(X\right)$. If $X$ is a countable infinite product of non-degenerate Peano continua, then the sequence ${\left({𝒟}_{\ge n}\left(C\left(X\right)\right)\right)}_{n=2}^{\infty }$ is $F_{\sigma }$-absorbing in $C\left(X\right)$. As a consequence, there is a homeomorphism $h:C\left(X\right)\to Q^{\infty }$ such that for all $n$, $h\left[\{A\in C\left(X\right):𝒟\left(A\right)\ge n+1\}\right]=B^n\times Q\times Q\times \cdots$, where $B$ denotes the pseudo boundary of the Hilbert cube $Q$. It follows that if $X$ is a countable infinite product of non-degenerate...

In every infinite-dimensional Fréchet space X, we construct a linear subspace E such that E is an $F_{\sigma \delta \sigma }$-subset of X and contains a retract R so that $R\times E^{\omega }$ is not homeomorphic to $E^{\omega }$. This shows that Toruńczyk’s Factor Theorem fails in the Borel case.