Alphabeta Math
TheoremStatement: Literature-sourcedProof: AI-generatedprecheck passverified 2026-09-23 (gpt-6-sol)
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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.

Fatou's lemma

Statement

Let (fn) be nonnegative measurable functions. Then ∫lim inf⁡n→∞fn dμ≤lim inf⁡n→∞∫fn dμ.

Facts & Assumptions

Given: A sequence (fn) of nonnegative measurable functions.

[L1]

Countable infima of measurable extended-real-valued functions are measurable, and monotone pointwise suprema are measurable (Closure properties of measurable functions used by the integral).

[L2]

Monotone convergence holds for the nonnegative integral (Monotone convergence for the integral).

Proof

technique · direct
1.1L1givenconstruct

For each n, define gn:=inf⁡k≥nfk. Then each gn is measurable by [L1], one has gn≤gn+1 and gn↑lim inf⁡nfn pointwise. Also gn≤fn for every n.

2.1step 1.1L2L3∎

By [L2] and step 1.1, ∫lim inf⁡nfn dμ=lim⁡n∫gn dμ. For every fixed n and all k≥n, one has gn≤gk≤fk. By [L3], ∫gn dμ≤inf⁡k≥n∫fk dμ. Taking the supremum over n and using monotone convergence on the left gives ∫lim inf⁡nfn dμ≤lim inf⁡n∫fn dμ, including infinite values.

Depends on

Used by

…and 4 more results.

Dependency tree · two levels

14 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