Alphabeta Math
TheoremStatement: Literature-sourcedProof: AI-generatedprecheck passaudited 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.

The modulus of an integral is bounded by the integral of the modulus

Statement

If f∈L1(μ), then ∣∫f dμ∣≤∫∣f∣ dμ.

Facts & Assumptions

Given: An integrable function f.

[L1]

The integral is linear on L1(μ) (The Lebesgue integral is linear on L1(μ)).

[L2]

Real and imaginary parts, complex conjugation, and modulus are as in Real and imaginary parts, complex conjugation, and modulus.

[L3]

Real and complex integrability are defined in Integrable real and complex functions, and their integrals.

Proof

technique · direct
1.1L1L3L4algebra

For real-valued f, the functions ∣f∣+f=2f+ and ∣f∣−f=2f− are nonnegative. Therefore [L1] and [L4] give 0≤∫(∣f∣+f) dμ=∫∣f∣ dμ+∫f dμ, 0≤∫(∣f∣−f) dμ=∫∣f∣ dμ−∫f dμ. So −∫∣f∣ dμ≤∫f dμ≤∫∣f∣ dμ, and hence ∣∫f dμ∣≤∫∣f∣ dμ.

2.1L1L2step 1.1L4algebra∎

For complex-valued f, let I:=∫f dμ. If I=0 there is nothing to prove. Otherwise set α:=I‾/∣I∣, so ∣α∣=1 by [L2]. Then ∣I∣=αI=∫αf dμ, and ∣Re⁡(αf)∣≤∣αf∣=∣f∣, so step 1.1 applies to the integrable real-valued function Re⁡(αf). Taking real parts gives ∣I∣=∫Re⁡(αf) dμ≤∫∣αf∣ dμ=∫∣f∣ dμ, because Re⁡z≤∣z∣ for every complex z.

Depends on

Used by

…and 14 more results.

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