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Leonard R. Rubin

Publications and source records attributed to Leonard R. Rubin.

3 recordsLinked to original sources

Alternate proofs for the $n$-dimensional resolution theorems

We present new, unified proofs for the cell-like, $\mathbb{Z}/p$-, and $\mathbb{Q}$-resolution theorems. Our arguments employ extensions that are much simpler then those used by our predecessors. The techniques allow us to solve problems involving cohomology groups by converting them into problems about homology groups. We provide a coordinated general topological method for constructing the maps needed to witness the resolution theorems simultaneously.

math.GT

Simplicial inverse sequences in extension theory

In extension theory, in particular in dimension theory, it is frequently useful to represent a given compact metrizable space X as the limit of an inverse sequence of compact polyhedra. We are going to show that, for the purposes of extension theory, it is possible to replace such an X by a better metrizable compactum Z. This Z will come as the limit of an inverse sequence of triangulated polyhedra with simplicial bonding maps that factor in a certain way. There will be a cell-like map from Z to X, and we shall show that if K is a CW-complex which is an absolute extensor for X, then K is also an absolute extensor for Z.

math.GT

Simultaneous Z/p-acyclic resolutions of expanding sequences

We prove the following Theorem: Let X be a nonempty compact metrizable space, let $l_1 \leq l_2 \leq...$ be a sequence of natural numbers, and let $X_1 \subset X_2 \subset...$ be a sequence of nonempty closed subspaces of X such that for each k in N, $dim_{Z/p} X_k \leq l_k < \infty$. Then there exists a compact metrizable space Z, having closed subspaces $Z_1 \subset Z_2 \subset...$, and a surjective cell-like map $π: Z \to X$, such that for each k in N, (a) $dim Z_k \leq l_k$, (b) $π(Z_k) = X_k$, and (c) $π| {Z_k}: Z_k \to X_k$ is a Z/p-acyclic map. Moreover, there is a sequence $A_1 \subset A_2 \subset...$ of closed subspaces of Z, such that for each k, $dim A_k \leq l_k$, $π|{A_k}: A_k\to X$ is surjective, and for k in N, $Z_k\subset A_k$ and $π|{A_k}: A_k\to X$ is a UV^{l_k-1}-map. It is not required that X be the union of all X_k, nor that Z be the union of all Z_k. This result generalizes the Z/p-resolution theorem of A. Dranishnikov, and runs parallel to a similar theorem of S. Ageev, R. Jiménez, and L. Rubin, who studied the situation where the group was Z.

math.GT