◀ ▲ ▶Branches / Topology / Definition: Limits and Accumulation Points of Sequences
Definition: Limits and Accumulation Points of Sequences
Let $(X,\mathcal O)$ be a topological space and let $(a_n)_{n\in\mathbb Z}$ be a sequence with $a_n\in X$ for all $n\in\mathbb Z$, and let $x\in X.$
If every open set $O\in\mathcal O$ containing $x$ contains
- ... all but finitely many terms of the sequence, then $x$ is called a limit point of the sequence $(a_n)_{n\in\mathbb Z},$ and we say that $(a_n)_{n\in\mathbb Z}$ converges to $x,$
- ... infinitely many terms of the sequence $(a_n)_{n\in\mathbb N}$, then $x$ is called an accumulation point of the sequence.
Notes
- A sequence converges against $x$ if only finitely many sequence members are located outside any given neighborhood of $x.$
- A sequence can be associated with its carrier set. Therefore, these definitions are specializations of the more general definitions of limits and $\omega$-accumulation points for sets.
- Sequences do not have condensation points, since they do not have uncountable many members, by definition.
Mentioned in:
Examples: 1
Parts: 2
Thank you to the contributors under CC BY-SA 4.0!
- Github:
-
References
Bibliography
- Forster Otto: "Analysis 2, Differentialrechnung im \(\mathbb R^n\), Gewöhnliche Differentialgleichungen", Vieweg Studium, 1984
Footnotes