Alphabeta Math
DefinitionDefinition: Literature-sourcedProof: Not applicableaudited 2026-08-27
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.

Integrable real and complex functions, and their integrals

Definition

Let f:X→R be measurable. Its positive and negative parts are f+:=max⁡{f,0},f−:=max⁡{−f,0}; they are measurable by Closure properties of measurable functions used by the integral and satisfy f=f+−f− and ∣f∣=f++f−.

The Lebesgue integral of a real measurable function is defined whenever at most one of ∫f+ dμ and ∫f− dμ is +∞, in which case ∫f dμ:=∫f+ dμ−∫f− dμ. The function is integrable when both integrals are finite, equivalently when ∫∣f∣ dμ<+∞.

For a complex measurable function h=u+iv with u=Re⁡h, v=Im⁡h (Real and imaginary parts, complex conjugation, and modulus), define h to be integrable when ∣h∣ is integrable, and then define ∫h dμ:=∫u dμ+i∫v dμ.

Depends on

Used by

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Dependency tree · two levels

12 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