import Mathlib.MeasureTheory.Order.Lattice
import Mathlib.Order.CompletePartialOrder
import Mathlib.Probability.Martingale.BorelCantelli
import Mathlib.Probability.Kernel.IonescuTulcea.Traj
import Mathlib.Probability.Process.FiniteDimensionalLaws
import Mathlib.Probability.HasCondDistrib
import Mathlib.MeasureTheory.Measure.ProbabilityMeasure
import Mathlib.Probability.Independence.Basic
import Mathlib.Probability.Independence.Conditional
import Mathlib.MeasureTheory.Measure.SubFinite
import Mathlib.Probability.Kernel.RadonNikodym
import Mathlib.Analysis.Normed.Ring.Basic
import Mathlib.MeasureTheory.Constructions.BorelSpace.Basic

/-! # Standalone extraction for `Bandits.gap_bestArm`
Definitions are copied verbatim; theorem proofs are replaced by `sorry`.
Auto-generated by Referee. -/

set_option quotPrecheck false

-- Namespace stubs (so later `open`s resolve).
namespace Finset
end Finset
namespace MeasureTheory
end MeasureTheory
namespace ProbabilityTheory
end ProbabilityTheory
namespace Learning
end Learning
namespace ENNReal
end ENNReal
namespace Bandits
end Bandits

-- ═══ ForMathlib.MeasureTheory.Order.Lattice ═══
section
open Finset
variable {α δ : Type*} [MeasurableSpace δ] [SemilatticeInf α] {m : MeasurableSpace α} [MeasurableInf₂ α]
attribute [to_dual existing] MeasurableInf₂
end

-- ═══ Online.Bandit.Regret ═══
section
open MeasureTheory ProbabilityTheory Filter Real Finset Learning
open scoped ENNReal NNReal
namespace Bandits
variable {𝓐 Ω : Type*} [DecidableEq 𝓐] {m𝓐 : MeasurableSpace 𝓐} {mΩ : MeasurableSpace Ω} {ν : Kernel 𝓐 ℝ} {A : ℕ → Ω → 𝓐} {R : ℕ → Ω → ℝ} {ω : Ω} {m n t : ℕ} {a : 𝓐}

/-- Gap of an action `a`: difference between the highest mean of the actions and the mean of `a`. -/
noncomputable
def gap (ν : Kernel 𝓐 ℝ) (a : 𝓐) : ℝ := (⨆ i, (ν i)[id]) - (ν a)[id]

section bestArm
variable [Fintype 𝓐] [Nonempty 𝓐]

/-- action with the highest mean. -/
noncomputable def bestArm (ν : Kernel 𝓐 ℝ) : 𝓐 :=
  (exists_max_image univ (fun a ↦ (ν a)[id]) (univ_nonempty_iff.mpr inferInstance)).choose

omit [DecidableEq 𝓐] in
@[simp]
lemma gap_bestArm : gap ν (bestArm ν) = 0 := sorry

end bestArm
end Bandits
end