# Local dimension

2010 Mathematics Subject Classification: Primary: 54F45 [MSN][ZBL]

of a normal topological space $X$

The topological invariant $\mathrm{locdim}(X)$, defined as follows. One says that $\mathrm{locdim}(X) \le n$, $n = -1,0,1,\ldots$ if for any point $x \in X$ there is a neighbourhood $O_x$ for which the Lebesgue dimension of its closure satisfies the relation $\dim \bar O_x \le n$. If $\mathrm{locdim}(X) \le n$ for some $n$, then the local dimension of $X$ is finite, so one writes $\mathrm{locdim}(X) < \infty$ and puts $$\mathrm{locdim}(X) = \min\{ n : \mathrm{locdim}(X) \le n \}$$

Always $\mathrm{locdim}(X) \le \dim(X)$; there are normal spaces $X$ with $\mathrm{locdim}(X) < \dim(X)$; in the class of paracompact spaces always $\mathrm{locdim}(X) = \dim(X)$. If in the definition of local dimension the Lebesgue dimension $\dim \bar O_x$ is replaced by the large inductive dimension $\mathrm{Ind} \bar O_x$, then one obtains the definition of the local large inductive dimension $\mathrm{locInd}(X)$.

See [a1] for a construction of a space with $\mathrm{locdim}(X) < \dim(X)$ and — as an application — a hereditarily normal space $Y$ with $\dim Y = 0$ yet $Y$ contains subspaces of arbitrary high dimension.