A point $P$ of a topological space $X$ is **isolated** if it is a neighbourhood of itself, in other words if the singleton subset $\{P\}$ is open.

More generally, a point $P$ of a subset $A$ of a space $X$ is **isolated** in $A$ if it is isolated when viewed as a point in the subspace $A$ with the subspace topology. More explicitly, for some neighbourhood $U$ of $P$ (in $X$), $U \cap A = \{P\}$.

The antithetical concept is that of an accumulation point.

Every function on $X$ is continuous at $P$ if $P$ is isolated.

Created on June 28, 2020 at 09:04:41. See the history of this page for a list of all contributions to it.