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Hereditarily aspherical compacta
Authors:Jerzy Dydak   Katsuya Yokoi
Affiliation:Department of Mathematics, University of Tennessee, Knoxville, Tennessee 37996 ; Institute of Mathematics, University of Tsukuba, Tsukuba-shi, Ibaraki, 305, Japan
Abstract:The notion of (strongly) hereditarily aspherical compacta introduced by Daverman (1991) is modified. The main results are: Theorem. If $Xin LC^{1}$ is a hereditarily aspherical compactum, then $Xin $ ANR. In particular, $X$ is strongly hereditarily aspherical.

Theorem. Suppose $f:Xto Y$ is a cell-like map of compacta and $f^{-1}(A)$ is shape aspherical for each closed subset $A$ of $Y$. Then
1.
Y is hereditarily shape aspherical,
2.
$f$ is a hereditary shape equivalence,
3.
$dim Xge dim Y$.

Theorem. Suppose $G$ is a group containing integers. Then the following conditions are equivalent:
1.
$dim Xle 2$ and $dim _{G}X=1$,
2.
$dim _{G*_{{mathbf Z} }G}X=1$.

Theorem. Suppose $G$ is a group containing integers. If $dim Xle 2$ and $dim _{G}X=1$, then $X$ is hereditarily shape aspherical.

Theorem. Let $X$ be a two-dimensional, locally connected and semilocally simply connected compactum. Then, for any compactum $Y$

begin{equation*}dim (X times Y) = dim X + dim Y.end{equation*}

Keywords:Dimension   cohomological dimension   aspherical compacta   ANR's   absolute extensors   cell-like maps
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