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Closure under absorption of half-factors

Proved
FiniteSplitGibbsMethodsII.halfFactorClosure

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

closurenonnegativityreflection-positivitysplit-weights

Let W(x,y)=∑a∈Acaϕa(x)ϕa(y)W(x,y)=\sum_{a\in A}c_a\phi_a(x)\phi_a(y)W(x,y)=∑a∈A​ca​ϕa​(x)ϕa​(y) be split data with finite AAA, and let h:X→Rh:X\to\mathbb Rh:X→R. Replacing ϕa(x)\phi_a(x)ϕa​(x) by h(x)ϕa(x)h(x)\phi_a(x)h(x)ϕa​(x) gives

W~(x,y)=h(x)h(y)W(x,y).\widetilde W(x,y)=h(x)h(y)W(x,y).W(x,y)=h(x)h(y)W(x,y).

If every ca≥0c_a\ge0ca​≥0, the coefficients remain nonnegative because they are unchanged. Separately, if hhh and WWW are pointwise nonnegative, then W~\widetilde WW is pointwise nonnegative. No pointwise positivity conclusion is asserted without the sign condition on hhh.

Preamble
import Definitions.Def_FiniteSplitGibbsMethodsII

open FiniteSplitGibbsMethodsII
Formal statement
theorem FiniteSplitGibbsMethodsII.halfFactorClosure :
    HalfFactorClosureGate := by sorry
Source
Finite closure lemma authored for this sequel from the split-weight representation published as Prove2Me definition bac19f55-f257-416b-bde1-568e139f34e9 and theorem 25912f71-137c-4b0d-b43b-3e25dcbd7163; source interface: LeanProofs commit dbf503b2909cc17787d40a21eb75a0c9354cc6ef, ReflectionPositivityInfraredBound.lean, lines 40--56. Exact local gate: HalfFactorClosureGate.
Read-back

What the Lean code literally says, in plain math · gpt-5

For every universe-level-0 pair of types X,AX,AX,A, every finite enumeration of AAA, every function h:X→Rh:X→ℝh:X→R, and every split-weight datum DDD on XXX indexed by AAA, let the absorbed datum keep DDD's coefficients and replace each feature D.feature(a,x)D.feature(a,x)D.feature(a,x) by h(x)D.feature(a,x)h(x)D.feature(a,x)h(x)D.feature(a,x). Then all three of the following hold: for every l,r∈Xl,r∈Xl,r∈X, its associated weight is exactly h(l)h(r)D.weight(l,r)h(l)h(r)D.weight(l,r)h(l)h(r)D.weight(l,r); if D.coefficient(a)≥0D.coefficient(a)≥0D.coefficient(a)≥0 for every a∈Aa∈Aa∈A, then every coefficient of the absorbed datum is nonnegative; and if h(x)≥0h(x)≥0h(x)≥0 for every x∈Xx∈Xx∈X and D.weight(l,r)≥0D.weight(l,r)≥0D.weight(l,r)≥0 for every l,r∈Xl,r∈Xl,r∈X, then the absorbed datum's associated weight is nonnegative for every l,r∈Xl,r∈Xl,r∈X. No finiteness assumption is made on XXX, and the third assertion has no coefficient-sign hypothesis. If AAA is empty, coefficient quantifiers are vacuous; if XXX is empty, every pointwise statement over XXX 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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