Sequential compactness and Euclidean Heine–Borel
In a metric space, K is compact exactly when every sequence in K has a subsequence converging to a point in K.
Key knowledge
In a metric space, K is compact exactly when every sequence in K has a subsequence converging to a point in K. For K⊂Rⁿ with its usual Euclidean metric, this is equivalent to K being closed and bounded. Closed and bounded is insufficient in general metric spaces.
Conditions and scope
- n is a fixed positive finite integer.
- The subsequence limit must belong to K, not merely its ambient space.
Sources · 1
References
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Evidence and review
Theorem7.4.11, Proposition7.4.9 and Heine–Borel Theorem7.4.14; coordinate extraction extends the displayed dimension2 proof to finite n.
2026-10-10 · Independent AI editorial review: All241 compact claims, hypotheses, displayed equations/conventions and all596 origin semantic links read; entire241-entry author exact-source inspection matrix and declared limitations reviewed. Prior105 actual inherited Mathematics/Information records read for whole-inventory breadth. Targeted independent primary sections are listed below; this does NOT claim every cited source body or every proof was independently re-read. This is AI reference-content review, not human disciplinary certification, exhaustive textbook reproduction or experimental replication. Receipt: mathematics-information-independent-content-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- math-metric-sequential-compactness
- Revision
- university-core.1
- Structured reference record
- University core expansion