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Uspekhi Mat. Nauk, 1976 Volume 31, Issue 5(191), Pages 185–190 (Mi rm3967)

On Aleksandrov's obstruction theorem

I. A. Shvedov


Abstract: The following two results ate proved.
Theorem 1. {\it Let $X$ be a subspace of a locally compact metric space with $\dim_{\mathscr G}X=p$, and $A$ the subset consisting of all points $a\in X$ such that $H^p(X,X\setminus U;\mathscr G)\ne 0$ for every sufficiently small open ball $U$ with centre at $a$. Then $\dim_{\mathscr G}A=p$}.
Theorem 2. {\it Let $X$ be a metric space, $\dim_{\mathscr G}X=p$, and $Y$ the subspace of $X$ consisting of all points $y\in X$ that have a basis of open neighbourhoods $\mathscr B(y)$ точки $y$ such that for each $U\in \mathscr B(y)$ the group $H^p(X,X\setminus U;\mathscr G)$ is not trivial. Then $\dim_{\mathscr G}Y=p$}.

UDC: 513.83

MSC: 22Bxx, 32C25, 20K30

Received: 01.03.1976


 English version:
Russian Mathematical Surveys, 1976, 31:5, 192–197

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© Steklov Math. Inst. of RAS, 2024