Compactness and finite subcovers
Compactness reduces every open cover to a finite one.
Key knowledge
A subset K of a topological space is compact if every open cover of K has a finite subcover. For subsets of R with its usual topology, compactness is equivalent to being closed and bounded.
Conditions and scope
- The cover is by sets open in the ambient topology.
- The closed-and-bounded criterion is not asserted for arbitrary metric spaces.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Definition 3.2.2 and Lemma 3.2.5: finite-open-cover compactness and ambient-space covers, without a Hausdorff requirement; Proposition 3.2.14: closed/bounded criterion in Rⁿ, used here only for R. Definition 5.32 and Theorem 5.36: sequential compactness and closed/bounded criterion on R.
2026-10-10 · General topological finite-subcover definition, ambient-cover equivalence and real-line criterion.
Entry details
Permanent link to this entry ↗- Record identity
- math-compactness
- Revision
- university-reference.1
- Structured reference record
- University reference