A simultaneous right-module average of a finite family of completely bounded maps
ProvedOAI.BoundedHochschild.KadisonRingrose.exists_finite_right_module_averageThroughout, is a unital C*-algebra with a partial order making it star-ordered, is a complex Banach space, and is an isometric conjugate-linear isomorphism, so is a von Neumann algebra with predual (the Lean hypothesis e). A family converges in the predual sense to (PredualTendsto) when for every . The hypothesis NoFiniteCentralSummand M says that a central projection whose corner is finite (every isometry of the corner is unitary) must vanish. Let be nontrivial with no finite central summand, and let be bounded linear maps with complete bounds . Then there are bounded maps with and for all , such that the family lies in the weak closure of the simultaneous averages over finite with (weakFamilyAverageOrbit).
Formalization Note The statement is verbatim from OpenAI's Lean development, with the listed Definitions imported in place of the upstream modules; the definitions are supporting code for this statement. Only the keyword lemma, where used upstream, becomes theorem, and a leading include ... in or omit ... in moves to the preamble. It is a step of the Lean proof of the vanishing of higher bounded Hochschild cohomology.
import Mathlib
import Definitions.Def_KadisonRingroseSupport2
namespace OAI
noncomputable section
open Topology
namespace BoundedHochschild.KadisonRingrose
open HochschildComparison
universe u
variable {M X : Type u} [CStarAlgebra M] [PartialOrder M] [StarOrderedRing M]
[NormedAddCommGroup X] [NormedSpace ℂ X] [CompleteSpace X]
theorem exists_finite_right_module_average [Nontrivial M]
(e : StrongDual ℂ X ≃ₗᵢ⋆[ℂ] M) (hno : NoFiniteCentralSummand M)
{n : ℕ} (T : Fin (n+1) → M →L[ℂ] M) (C : Fin (n+1) → ℝ)
(hT : ∀ i, CompletelyBoundedEstimate (T i) (C i)) :
∃ S : Fin (n+1) → M →L[ℂ] M,
(∀ i, ‖S i‖ ≤ C i ∧ ∀ a b, S i (a*b) = S i a * b) ∧
(fun i => weakOperatorImage e (S i)) ∈ weakFamilyAverageOrbit e T := by
sorry
end BoundedHochschild.KadisonRingrose
end
end OAI