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Corollary 4.5 — K2=K2p=K2μ=K2sK_2 = K_2^p = K_2^\mu = K_2^sK2​=K2p​=K2μ​=K2s​ with K2K_2K2​ over the support of (p,T)(p,T)(p,T)

Proved
Wets1974.Feasibility.K2_eq_feasibility_sets

by mikedeng1 · Sep 29, 2026 · Mathlib 0df444a (Lean v4.33.1)

feasibilityp2o-batch-p200bp2o-gran-per-chapterp2o-plan-paperp2o-v1recoursestochastic-programming

In the setting of Theorem 4.1 (fixed recourse matrix WWW of size mˉ×nˉ\bar m \times \bar nmˉ×nˉ, random data ξ=(c,q,p,T)\xi = (c, q, p, T)ξ=(c,q,p,T) with law μ\muμ), let Ξ~p,T\tilde\Xi_{p,T}Ξ~p,T​ be the support of the marginal distribution of (p(ξ),T(ξ))(p(\xi), T(\xi))(p(ξ),T(ξ)) and, for ζ=(p,T)\zeta = (p, T)ζ=(p,T), let K2(ζ)={x∣p−Tx∈pos⁡W}K_2(\zeta) = \{x \mid p - Tx \in \operatorname{pos} W\}K2​(ζ)={x∣p−Tx∈posW}, where pos⁡W={Wy∣y≥0}\operatorname{pos} W = \{Wy \mid y \ge 0\}posW={Wy∣y≥0}. Put

K2=⋂ζ∈Ξ~p,TK2(ζ)={x∣p−Tx∈pos⁡W for all (p,T)∈Ξ~p,T}.K_2 = \bigcap_{\zeta \in \tilde\Xi_{p,T}} K_2(\zeta) = \{x \mid p - Tx \in \operatorname{pos} W \text{ for all } (p, T) \in \tilde\Xi_{p,T}\}.K2​=ζ∈Ξ~p,T​⋂​K2​(ζ)={x∣p−Tx∈posW for all (p,T)∈Ξ~p,T​}.

If ξ\xiξ satisfies the weak covariance condition (Definition 2.2) and WWW has full row rank, then

K2=K2p=K2μ=K2s,K_2 = K_2^p = K_2^\mu = K_2^s,K2​=K2p​=K2μ​=K2s​,

with K2pK_2^pK2p​, K2μK_2^\muK2μ​, K2sK_2^sK2s​ as in Theorem 4.1.

The new content over Theorem 4.1 is that the support of the (p,T)(p,T)(p,T)-marginal may replace the support of ξ\xiξ: feasibility depends only on the right-hand side and technology matrix. From here on the paper writes K2K_2K2​ for this common set.

Formalization Note. Ξ~p,T\tilde\Xi_{p,T}Ξ~p,T​ is the support of the pushforward of μ\muμ under the coordinate projection ξ↦(p,T)\xi \mapsto (p, T)ξ↦(p,T), which is continuous and hence measurable. Full row rank of WWW is the paper's standing assumption (p. 312).

Preamble
import Mathlib
import Definitions.Def_Wets1974_Feasibility_Model
Formal statement
namespace Wets1974.Feasibility

open MeasureTheory

/-- Corollary 4.5, p. 316: under the weak covariance condition (Definition 2.2) and the
standing assumption that `W` has full row rank (p. 312), `K₂ = K₂^p = K₂^μ = K₂^s`, where
`K₂ = ⋂_{ζ ∈ Ξ̃_{p,T}} K₂(ζ)`. -/
theorem K2_eq_feasibility_sets {n nb mb : ℕ} (μ : Measure (DataSpace n nb mb))
    [IsProbabilityMeasure μ] (W : Matrix (Fin mb) (Fin nb) ℝ)
    (hW : W.rank = mb) (hcov : WeakCovariance μ) :
    K2 μ W = K2supp μ W ∧ K2supp μ W = K2mu μ W ∧ K2mu μ W = K2s μ W := by sorry

end Wets1974.Feasibility
Source
Wets, Stochastic Programs with Fixed Recourse: The Equivalent Deterministic Program, SIAM Review 16(3), 1974, p. 316, Corollary 4.5 (with Eq. (4.4))
Human review
  • Endorsed by Shuze Chen · Oct 1, 2026

    Confirmed by the moderator at approval.

  • Endorsed by mikedeng1 · Oct 1, 2026

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

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