import Mathlib
import OAI.Computability.VertexCover.Games.Basic

namespace OAI

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namespace UniqueGames.Foundations.Games

open scoped BigOperators

noncomputable section

namespace Game

variable {Q₁ Q₂ A₁ A₂ : Type*}
  [Fintype Q₁] [Fintype Q₂] [Fintype A₁] [Fintype A₂]
  [Nonempty A₁] [Nonempty A₂]

def value (G : Game Q₁ Q₂ A₁ A₂) : ℝ := by
  classical
  exact Finset.univ.sup' Finset.univ_nonempty G.success

theorem success_le_value (G : Game Q₁ Q₂ A₁ A₂)
    (strategy : Strategy Q₁ Q₂ A₁ A₂) : G.success strategy ≤ G.value := by
  classical
  exact Finset.le_sup' G.success (Finset.mem_univ strategy)

theorem value_le_iff (G : Game Q₁ Q₂ A₁ A₂) (bound : ℝ) :
    G.value ≤ bound ↔ ∀ strategy : Strategy Q₁ Q₂ A₁ A₂, G.success strategy ≤ bound := by
  classical
  simp [value, Finset.sup'_le_iff]

theorem exists_optimal_strategy (G : Game Q₁ Q₂ A₁ A₂) :
    ∃ strategy : Strategy Q₁ Q₂ A₁ A₂, G.success strategy = G.value := by
  classical
  obtain ⟨strategy, _, h⟩ := Finset.exists_mem_eq_sup'
    (s := (Finset.univ : Finset (Strategy Q₁ Q₂ A₁ A₂))) Finset.univ_nonempty G.success
  exact ⟨strategy, h.symm⟩

theorem value_nonnegative (G : Game Q₁ Q₂ A₁ A₂) : 0 ≤ G.value := by
  obtain ⟨strategy, h⟩ := G.exists_optimal_strategy
  rw [← h]
  exact G.success_nonnegative strategy

theorem value_le_one (G : Game Q₁ Q₂ A₁ A₂) : G.value ≤ 1 :=
  (G.value_le_iff 1).2 G.success_le_one

theorem randomized_success_le_value (G : Game Q₁ Q₂ A₁ A₂)
    {Seed : Type*} [Fintype Seed] (seedLaw : FiniteDistribution Seed)
    (strategies : Seed → Strategy Q₁ Q₂ A₁ A₂) :
    seedLaw.expectation (fun seed => G.success (strategies seed)) ≤ G.value := by
  unfold FiniteDistribution.expectation
  calc
    _ ≤ ∑ seed, seedLaw.weight seed * G.value := by
      apply Finset.sum_le_sum
      intro seed _
      exact mul_le_mul_of_nonneg_left (G.success_le_value _) (seedLaw.nonnegative seed)
    _ = G.value := by rw [← Finset.sum_mul, seedLaw.normalized, one_mul]

omit [Nonempty A₁] [Nonempty A₂] in
theorem success_repetition_zero (G : Game Q₁ Q₂ A₁ A₂)
    (strategy : Strategy (Fin 0 → Q₁) (Fin 0 → Q₂) (Fin 0 → A₁) (Fin 0 → A₂)) :
    (G.repetition 0).success strategy = 1 := by
  have h : (G.repetition 0).wins strategy = fun _ => true := by
    funext questions
    simp [wins, repetition]
  unfold success
  rw [h, FiniteDistribution.probability_true]

@[simp] theorem value_repetition_zero (G : Game Q₁ Q₂ A₁ A₂) :
    (G.repetition 0).value = 1 := by
  obtain ⟨strategy, h⟩ := (G.repetition 0).exists_optimal_strategy
  rw [← h]
  exact G.success_repetition_zero strategy

theorem pow_value_le_repetition_value (G : Game Q₁ Q₂ A₁ A₂) (n : Nat) :
    G.value ^ n ≤ (G.repetition n).value := by
  obtain ⟨strategy, h⟩ := G.exists_optimal_strategy
  rw [← h, ← G.success_repeatStrategy strategy n]
  exact (G.repetition n).success_le_value (repeatStrategy strategy n)

theorem value_le_of_localSimulation {R₁ R₂ B₁ B₂ : Type*}
    [Fintype R₁] [Fintype R₂] [Fintype B₁] [Fintype B₂]
    [Nonempty B₁] [Nonempty B₂]
    (G : Game Q₁ Q₂ A₁ A₂) (H : Game R₁ R₂ B₁ B₂)
    (questionMap₁ : Q₁ → R₁) (questionMap₂ : Q₂ → R₂)
    (answerMap₁ : Q₁ → B₁ → A₁) (answerMap₂ : Q₂ → B₂ → A₂)
    (questionLaw : H.questions =
      G.questions.pushforward (fun q => (questionMap₁ q.1, questionMap₂ q.2)))
    (acceptance : ∀ x y a b,
      H.accepts (questionMap₁ x) (questionMap₂ y) a b = true →
      G.accepts x y (answerMap₁ x a) (answerMap₂ y b) = true) :
    H.value ≤ G.value := by
  apply (H.value_le_iff _).2
  intro strategy
  exact (G.success_le_of_localSimulation H questionMap₁ questionMap₂
    answerMap₁ answerMap₂ questionLaw acceptance strategy).trans (G.success_le_value _)

end Game

end

end UniqueGames.Foundations.Games

end


end
end
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end
end

end OAI