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.
- Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
- AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
- AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.
These labels describe origin, not correctness: citations and verification chips remain separate evidence.
Finite and countable subadditivity of measures
Statement
Let be a measure and let be measurable. Then
For every one also has
including , where both sides are .
Facts & Assumptions
Given: A measure and a sequence of measurable sets.
A measure is countably additive on pairwise disjoint measurable sequences (Measures on sigma-algebras).
If are measurable, then (Measures are monotone).
A nonnegative extended series is the supremum of its finite partial sums, beginning with the empty sum (Series in the nonnegative extended real line).
Every nonempty subset of has a least element (The well-ordering principle).
Proof
Define . Then every is measurable, the are pairwise disjoint, and .
The unions of the two sequences agree: if , then the nonempty set has a least member , and the definition gives ; the reverse inclusion follows from .
Countable additivity, monotonicity, and the definition of a nonnegative series give .
For , apply step 2.1 to the sequence ; its union and sum are the displayed finite union and finite sum, and when they are both empty and equal to .
Depends on
Used by
- Brownian paths are locally Holder below one half Corollary
- Dominated convergence is a Vitali corollary Corollary
- Polar integration may discard the cut locus Corollary
- Submartingale doob decomposition has increasing compensator Corollary
- The Solovay model has no Vitali or Bernstein set Corollary
- Topological recurrence on second-countable spaces Corollary
- A nonintegrable observable with divergent ergodic averages Counterexample
- A null set can fail to be the discontinuity set of any function Counterexample
- Assuming Choice, a proper subgroup of (ℝ,+) can be nonmeasurable Counterexample
- Cantor function has singular distributional derivative Counterexample
- Hilbert transform does not map L-infinity to L-infinity Counterexample
- Borel master codes for null and meagre sets Definition
- Conditional law given a random element Definition
- Direct integral of a measurable Hilbert field Definition
- A positive-measure compact set can miss part of every interval Example
- An open dense set of measure less than 1 is the monotone L¹-limit of Riemann integrable indicators, but its indicator is not Riemann integrable Example
- Empirical laws of a finite valued iid sample Example
- For every positive ε there is a dense open subset of (0,1) of Lebesgue measure below ε Example
- Likelihood ratio martingale Example
- Mollification of a complex two-step function Example
- Strong law for empirical indicator averages Example
- The Dirichlet function satisfies Lusin's conclusion without being continuous anywhere Example
- The graph of a continuous function ℝ→ℝ is Lebesgue null in ℝ² Example
- Birkhoff's theorem requires integrability False statement
- False: measure-preserving transformations are invertible False statement
- A C¹ diffeomorphism maps Lebesgue null sets to Lebesgue null sets Lemma
- A universal Martin-Löf test exists Lemma
- Approximation in symmetric difference by a generating algebra Lemma
- Assuming countable choice, an infinite-measure set in a semifinite measure space has arbitrarily large finite-measure subsets Lemma
- Assuming countable choice, simple approximants to a measurable function can be made uniformly convergent on a large closed set Lemma
- Assuming countable choice, simple functions are continuous on a large closed core Lemma
- Basic identities for a probability measure Lemma
- Cauchy sequences in probability have a measurable limit Lemma
- Chacon partial maps extend to an invertible map mod null sets Lemma
- Complex Lq norm recovery from finite simple dual tests Lemma
- Conditional expectation process is a martingale Lemma
- Countable boundary null partitions of a separable metric space Lemma
- Diagonal multipliers form a von Neumann algebra Lemma
- Finite-measure growth increment lemma Lemma
- Hedberg pointwise inequality for Riesz potentials Lemma
…and 59 more results.
Dependency tree · two levels
16 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
- S. Axler, Measure, Integration & Real Analysis, Theorem 2.58 (standard reference, not scraped)