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C_c(X) is dense in L^p(mu) for a Radon measure
Statement
Assume Dependent Choice (The axiom of dependent choice: a relation in which every element is related to something admits an -indexed chain). If is a Radon measure on an LCH space and , then is dense in .
Facts & Assumptions
Given: DC, is Radon and .
Finite-measure-support simple functions are dense in . (Simple functions with finite-measure support are dense in for )
Under the stated DC premise, LCH cutoffs exist between compact and open sets (LCH Urysohn cutoff). Proof 2.1 is the exact use of DC.
Proof
It suffices by [L1] to approximate when . [L1, choose] Given , outer regularity gives open with , and inner regularity of gives compact with .
Choose with by [L2]. [step 1.1, L2] Then Since both indicators take only the values zero and one and their union is , while , the error is bounded by the indicator of that union. Hence Thus .
Approximate the finitely many indicator terms of a simple function separately and sum the resulting functions. Then use [L1] and the triangle inequality.
Depends on
- The axiom of dependent choice: a relation in which every element is related to something admits an $\mathbb{N}$-indexed chain
- Radon measure on an LCH space
- Compact support, $C_c(X)$, and $C_0(X)$
- LCH Urysohn cutoff
- Simple functions with finite-measure support are dense in $L^p(\mu)$ for $1 \le p < \infty$
- The space $L^p(\mu)$ as the quotient by null functions
Used by
- Bounded Sobolev sequences have strongly convergent subsequences with the weak limit as limit Corollary
- Hilbert and Riesz transforms are bounded on weighted L-p Corollary
- Left and right regular representations on L2(G) Definition
- Multiplicity-two diagonal representation Example
- C_c(X) is dense in Lⁱnfinity(mu) for every Radon measure False statement
- Central continuous approximate identities Lemma
- Compact-open neighbourhoods on the dual give a neighbourhood basis on the group Lemma
- Compactly supported nonnegative transform bumps on the dual Lemma
- Completeness of the complex Haar L1 and L2 spaces and density of Cc Lemma
- Density of averaged covariant generators Lemma
- Differentiation of L-one functions for a doubling weight Lemma
- L¹ of an LCA group is a commutative Banach star algebra under convolution Lemma
- Nonzero multiplicative functionals on L¹ of an LCA group are Fourier evaluations Lemma
- Positive convolution squares form a dense inversion core Lemma
- Positive definite functions give positive bounded functionals on the transform core Lemma
- Quadratic path energy is lower semicontinuous Lemma
- Scalar unitisation of L¹ of an LCA group: characters, spectrum and identity criterion Lemma
- Smooth compactly supported tests are dense for finite Radon L2 measures Lemma
- Spherical harmonics form a complete basis with the addition formula Lemma
- The character topology on L¹ of an LCA group is the compact-open topology Lemma
- The Plancherel transform range is dense in L² of the dual Lemma
- Translation continuity and normalised local approximate identities on an LCA group Lemma
- Unitary intertwiners preserve direct-integral fiber dimension Lemma
- Cyclic spectral representation Theorem
- Fourier inversion for integrable transforms on LCA groups Theorem
- Plancherel isometric extension on LCA groups Theorem
- Pontryagin biduality: the evaluation map is a topological isomorphism Theorem
- Riemann-Lebesgue lemma on LCA groups Theorem
- Spectral multiplicity model for separably acting abelian von Neumann algebras Theorem
- Superposition for finite-action Euclidean continuity equations Theorem
- Weighted L-p bounds for standard Calderon-Zygmund maximal truncations Theorem
Dependency tree · two levels
30 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Donald L. Cohn, Measure Theory, 2nd ed., Chapter 7 (standard reference, not scraped)