How statement and proof provenance work
The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
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- AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
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Eventual access is uniform on the trimmed compact inside core
Statement
Let be a manifold with nonempty compact boundary , equipped with a metric inducing its manifold topology, and write . Let be a compact inside region containing an open neighborhood of , and denote its outer boundary by , the topological boundary relative to . Set . Suppose , where is an ambient manifold and the inclusion is continuous for the subspace topology inherited from . Let be open subsets of with for , and suppose that for every there is such that for all . Then for every sufficiently small there is such that for all . Moreover is compact and disjoint from , and there is an open section neighborhood of the whole outer boundary with for every .
Statement references
Facts & Assumptions
The interior of a manifold with boundary is . A compatible metric has the manifold open sets as its metric open sets. The relative topological boundary of is , and is open. Interior and boundary of a manifold with boundary Metric space: d(x,y) = 0 iff x = y, symmetry, and the triangle inequality; pseudometric and ultrametric The metric topology: a set is open when every one of its points has a ball around it inside the set; closed means open complement Interior, closure, boundary, limit point, isolated point and dense subset of a metric space
For a nonempty subset of a metric space, is a finite real number and . Bounded subset, diameter, distance from a point to a set, and distance between two sets in a metric space |d(x,A) - d(y,A)| ≤ d(x,y), so the distance to a fixed nonempty set is 1-Lipschitz
Compactness is intrinsic to the subspace topology. On a metric space, topological and metric compactness agree. Compact metric subsets are closed, and a closed subset of a compact metric space is compact. Open cover, subcover, and compact topological space; a compact subset is a subspace that is compact in its own right For a metric space with its metric topology, compactness in the topological sense is compactness in the metric sense, and the two notions of compact subset coincide A compact subset of a metric space is closed and bounded A closed subset of a compact metric space is compact
Subspace open sets are traces of ambient open sets, and subspace topologies are transitive. For a continuous inclusion, inverse images of ambient open sets are open. An indexed family of open sets of a topological space covering a compact subset has finitely many indices whose sets cover it, unless the subset is empty. Subspace topology: the traces of the open sets, its closed sets and its bases, the continuity of the inclusion, and the characteristic property of a map into a subspace Continuity of a map of topological spaces at a point and globally A subspace is compact exactly when every family of open subsets of the ambient space covering it, indexed or not, has finitely many members covering it
A finite nonempty list of real numbers has a largest member. A continuous real function on a nonempty compact metric space attains a minimum. Every nonempty finite set of reals has a maximum and a minimum A continuous real-valued function on a nonempty compact metric space is bounded and attains a greatest and a least value
Proof
Given: The hypotheses in the Statement.
Goal: Establish the trimmed-core containment and the persistent open neighborhood of the outer boundary.
By compatibility of and [F3], and are compact metric subsets of , hence closed. Since contains an open neighborhood of , we have . Closedness of implies : a point outside has a metric ball in its open complement and so is not adherent to . Thus is closed in , compact by [F3], and contained in . Also is open in because is closed.
By [F2] and , is finite and -Lipschitz, hence continuous: gives . It vanishes on . If , closedness of gives a ball of radius about disjoint from , so for every and . For any , is closed in : at a point with , the Lipschitz bound keeps throughout a sufficiently small ball. By [F3], is compact, and it avoids . Its topology inherited from equals that inherited from , by transitivity of subspace topologies in [F4]; hence it remains intrinsically compact as a subset of .
Fix and let . The continuity of the inclusion makes open in . Eventual entry applies to every point of , so the indexed family covers . By its compactness and the indexed ambient-cover criterion in [F4], if there are finitely many indices whose sets cover it. Put , which exists by [F5]. Increasingness gives for every . If , take and the same containment is automatic.
If , its compactness and the continuity of allow [F5] to give attained at a point of . Step 2.1 and give . For , we have . Consequently contains , is open in by [F4], and is open in because is open. Increasingness gives for all . If , take and ; the neighborhood assertion is vacuous and the trimmed-core containment still follows from step 3.1. This proves both conclusions, with a single neighborhood valid at all later times.
Depends on
- Topological manifolds with boundary
- Interior and boundary of a manifold with boundary
- Metric space: d(x,y) = 0 iff x = y, symmetry, and the triangle inequality; pseudometric and ultrametric
- The metric topology: a set is open when every one of its points has a ball around it inside the set; closed means open complement
- Interior, closure, boundary, limit point, isolated point and dense subset of a metric space
- Bounded subset, diameter, distance from a point to a set, and distance between two sets in a metric space
- |d(x,A) - d(y,A)| ≤ d(x,y), so the distance to a fixed nonempty set is 1-Lipschitz
- Open cover, subcover, and compact topological space; a compact subset is a subspace that is compact in its own right
- For a metric space with its metric topology, compactness in the topological sense is compactness in the metric sense, and the two notions of compact subset coincide
- A compact subset of a metric space is closed and bounded
- A closed subset of a compact metric space is compact
- Subspace topology: the traces of the open sets, its closed sets and its bases, the continuity of the inclusion, and the characteristic property of a map into a subspace
- Continuity of a map of topological spaces at a point and globally
- A subspace is compact exactly when every family of open subsets of the ambient space covering it, indexed or not, has finitely many members covering it
- Every nonempty finite set of reals has a maximum and a minimum
- A continuous real-valued function on a nonempty compact metric space is bounded and attains a greatest and a least value
Dependency tree · 2 levels
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