arXiv subjects
Publications and source records attributed to Alex Chigogidze.
We identify a class of subspaces of ordered spaces $\mathcal L$ for which the following statement holds: If $f:X\to L\in \mathcal L$ is a continuous bijections of a zero-dimensional space $X$, then $f$ can be re-routed via a zero-dimensional subspace of an ordered space that has weight not exceeding that of $L$.
We prove a version of $Z$-set unknotting theorem for uncountable products of real numbers.
It is shown that for a map $f \colon X \to Y$ of compact spaces the unital $\ast$-homomorphism $C(f) \colon C(Y) \to C(X)$ is projective in the category $\operatorname{Mor}({\mathcal C}^{1})$ precisely when $X$ is a dendrite and $f$ is either homeomorphism or a constant.
Some generalizations of the classical Hurewicz formula are obtained for extension dimension and C-spaces.
We introduce a concept of the bounded rank (with respect to a positive constant) for unital C*-algebras as a modification of the usual real rank and present a series of conditions insuring that bounded and real ranks coincide. These observations are then used to prove that for a given $n$ and $K > 0$ there exists a separable unital C*-algebra $Z_{n}^{K}$ such that every other separable unital C*-algebra of bounded rank with respect to $K$ at most $n$ is a quotient of $Z_{n}^{K}$.
It is well-known that every commutative separable unital C*-algebra of real rank zero is a quotient of the C*-algebra of all compex continous functions defined on the Cantor cube. We prove a non-commutative version of this result by showing that the class of all separable unital C*-algebras of real rank zero concides with the class of quotients of a certain separable unital C*-algebra of real-rank zero.
We show that a complemented subspace of a locally convex direct sum of an uncountable collection of Banach spaces is a locally convex direct sum of complemented subspaces of countable subsums. As a corollary we prove that a complemented subspace of a locally convex direct sum of arbitrary collection of $\ell_{1}(Γ)$-spaces is isomorphic to a locally convex direct sum of $\ell_{1}(Γ)$-spaces.
We show that complemented subspaces of uncountable products of Banach spaces are products of complemented subspaces of countable subproducts.
It is shown that every continuous homomorphism of Arens-Michael algebras can be obtained as the limit of a morphism of certain projective systems consisting of Fréchet algebras. Based on this we prove that a complemented subalgebra of an uncountable product of Fréchet algebras is topologically isomorphic to the product of Fréchet algebras. These results are used to characterize injective objects of the category of locally convex topological vector spaces. Dually, it is shown that a complemented subspace of an uncountable direct sum of Banach spaces is topologically isomorphic to the direct sum of ({\bf LB})-spaces. This result is used to characterize projective objects of the above category.
We investigate topological AE(0) -groups class of which contains the class of Polish groups as well as the class of all locally compact groups. We establish the existence of an universal AE(0) -group of a given weight as well as the existence of an universal action of AE(0) -group of a given weight on a AE(0) -space of the same weight. A complete characterization of closed subgroups of powers of the symmetric group is obtained. It is also shown that every AE (0)-group is Baire isomorphic to the product of Polish groups. These results are obtained by using the spectral descriptions of AE(0)-groups which are presented in Section 3.
We give a topological characterization of the n-dimensional pseudo-boundary of the (2n+1)-dimensional Euclidean space.
Extension dimension is characterized in terms of $ω$-maps. We apply this result to prove that extension dimension is preserved by refinable maps between metrizable spaces. It is also shown that refinable maps preserve some infinite-dimensional properties.
We show that the n-homotopy category of connected (n+1)-dimensional Menger manifolds is isomorphic to the homotopy category of connected Hilbert cube manifolds whose k-dimensional homotopy groups are trivial for each k > n.
For any countable $CW$-complex $K$ and a cardinal number $τ\geqω$ we construct a completely metrizable space $X(K,τ)$ of weight $τ$ with the following properties: $\e X(K,τ)\leq K$, $X(K,τ)$ is an absolute extensor for all normal spaces $Y$ with $\e Y\leq K$, and for any completely metrizable space $Z$ of weight $\leqτ$ and $\e Z\leq K$ the set of closed embeddings $Z\to X(K,τ)$ is dense in the space $C(Z,X(K,τ))$ of all continuous maps from $Z$ into $X(K,τ)$ endowed with the limitation topology. This result is applied to prove the existence of universal spaces for all metrizable spaces of given weight and with a given cohomological dimension.
We introduce the concept of a direct $C_ω^{\ast}$-system and show that every non-separable unital $C^{\ast}$-algebra is the limit of essentially unique direct $C_ω^{\ast}$-system. This result is then applied to the problem of characterization of projective unital $C^{\ast}$-algebras. It is shown that a non-separable unital $C^{\ast}$-algebra $X$ of density $τ$ is projective if and only if it is the limit of a well ordered direct system ${\mathcal S}_{X} = \{X_α, i_α^{α+1}, α< τ\}$ of length $τ$, consisting of unital projective $C^{\ast}$-subalgebras $X_α$ of $X$ and doubly projective homomorphisms (inclusions) $i_α^{α+1} \colon X_α \to X_{α+1}$, $α< τ$, so that $X_{0}$ is separable and each $i_α^{α+1}$, $α< τ$, has a separable type. In addition we show that a doubly projective homomorphism $f \colon X \to Y$ of unital projective $C^{\ast}$-algebras has a separable type if and only if there exists a pushout diagram \[ \begin{CD} X @>f>> Y @A{p}AA @AA{q}A X_{0} @>f_{0}>> Y_{0}, \end{CD} \] \noindent where $X_{0}$ and $Y_{0}$ are separable unital projective $C^{\ast}$-algebras and the homomorphisms $i_{0} \colon X_{0} \to Y_{0}$, $p \colon X_{0} \to X$ and $q \colon Y_{0} \to Y$ are doubly projective. These two results provide a complete characterization of non-separable projective unital $C^{\ast}$-algebras in terms of separable ones.
We characterize AE(0)-spaces that are Baire isomorphic to the powers of the real line.
We show that for each countable simplicial complex P the following conditions are equivalent: (1) $P \in AE(X)$ iff $P \in AE(βX)$ for any space X; (2) There exists a P-invertible map of a metrizable compactum X with $P \in AE(X)$ onto the Hilbert cube.
It is shown, under the assumption of Jensen's principle $\lozenge$, that if for a complex L with $[L] \geq [S^{4}]$ there exists a metrizable compactum whose extension dimension is L, then there exists a differentiable, countably compact, perfectly normal and hereditarily separable 4-manifold whose extension dimension is also [L].