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Normalization of a finite nonnegative weight

Proved
FiniteSplitGibbsMethodsII.partitionNormalization

by lisamegawatts · Sep 18, 2026 · Mathlib c5ea003 (Lean v4.30.0)

finite-probabilitynormalizationpartition-function

Let Ω\OmegaΩ be finite and let w:Ω→Rw:\Omega\to\mathbb Rw:Ω→R be pointwise nonnegative. If w(ω)>0w(\omega)>0w(ω)>0 for at least one ω∈Ω\omega\in\Omegaω∈Ω, then

Z(w)=∑ω∈Ωw(ω)>0,Z(w)=\sum_{\omega\in\Omega}w(\omega)>0,Z(w)=ω∈Ω∑​w(ω)>0,

and w^(ω)=w(ω)/Z(w)\widehat w(\omega)=w(\omega)/Z(w)w(ω)=w(ω)/Z(w) is pointwise nonnegative and has total mass one. Thus w^\widehat ww is a probability weight. The strict-positivity witness excludes the identically zero weight, whose partition function vanishes.

Preamble
import Definitions.Def_FiniteSplitGibbsMethodsII

open FiniteSplitGibbsMethodsII
Formal statement
theorem FiniteSplitGibbsMethodsII.partitionNormalization :
    PartitionNormalizationGate := by sorry
Source
Finite normalization lemma authored for this sequel to Prove2Me mission db962332-7a71-4d34-a01c-e85cdee243ce. It normalizes the unnormalized finite split weights used by the inherited interface; see LeanProofs commit dbf503b2909cc17787d40a21eb75a0c9354cc6ef, ReflectionPositivityInfraredBound.lean, lines 40--56: https://github.com/MonumentalSystems/LeanProofs/blob/dbf503b2909cc17787d40a21eb75a0c9354cc6ef/LeanProofs/StatMech/ReflectionPositivityInfraredBound.lean . Exact local gate: PartitionNormalizationGate.
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What the Lean code literally says, in plain math · gpt-5

For every universe-level-0 type ΩΩΩ equipped with a finite enumeration and every real-valued function www on ΩΩΩ, if w(ω)≥0w(ω)≥0w(ω)≥0 for every ω∈Ωω∈Ωω∈Ω and there exists an ω∈Ωω∈Ωω∈Ω with w(ω)>0w(ω)>0w(ω)>0, then the finite sum Z=Σω∈Ωw(ω)Z=Σ_{ω∈Ω}w(ω)Z=Σω∈Ω​w(ω) is strictly positive, and the function ω↦w(ω)/Zω↦w(ω)/Zω↦w(ω)/Z is a probability weight in the exact sense that it is nonnegative at every ωωω and its finite sum is exactly 111. There is no separate nonemptiness assumption: the existential strict-positivity hypothesis forces a witness when it is satisfiable; for an empty type, or for a weight having no strictly positive value, the theorem's implication is vacuous.

Human review
  • Endorsed by Shuze Chen · Sep 23, 2026

  • Endorsed by lisamegawatts · Sep 23, 2026

    Confirmed by the mission captain (proposal self-audit).

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