limit point


Let X be a topological spaceMathworldPlanetmath, and let AX. An element xX is said to be a limit pointMathworldPlanetmathPlanetmath of A if every open set containing x also contains at least one point of A distinct from x. Note that we can often take a nested sequence of open such sets, and can thereby construct a sequence of points which converge to x, partially motivating the terminology ”limit” in this case.

Equivalently:

  • x is a limit point of A if and only if there is a net in A converging to x which is not residually constant.

  • x is a limit point of A if and only if there is a filter on A converging (http://planetmath.org/filter) to x.

  • If X is a metric (or first countable) space, x is a limit point of A if and only if there is a sequence of points in A{x} converging to x.

Title limit point
Canonical name LimitPoint
Date of creation 2013-03-22 12:06:51
Last modified on 2013-03-22 12:06:51
Owner mathcam (2727)
Last modified by mathcam (2727)
Numerical id 15
Author mathcam (2727)
Entry type Definition
Classification msc 54A99
Synonym accumulation pointMathworldPlanetmath
Synonym cluster point
Related topic AlternateStatementOfBolzanoWeierstrassTheorem