  24@[simp] theorem narrativeCost_self (a : NarrativeBeat) : narrativeCost a a = 0 := by
  25  simp [narrativeCost]
  26
  27theorem narrativeCost_symm (a b : NarrativeBeat) : narrativeCost a b = narrativeCost b a := by
  28  by_cases h : a = b
  29  · subst h; simp [narrativeCost]
  30  · have h' : b ≠ a := by intro hb; exact h hb.symm
  31    simp [narrativeCost, h, h']
  32
  33def narrativeInterpret (n : LogicNat) : NarrativeBeat :=
  34  LogicNat.toNat n
  35
  36/-- Narrative realization as beat-count comparison. -/
  37def narrativeRealization : LogicRealization where
  38  Carrier := NarrativeBeat
  39  Cost := Nat
  40  zeroCost := inferInstance
  41  compare := narrativeCost
  42  zero := 0
  43  step := Nat.succ
  44  Orbit := LogicNat
  45  orbitZero := LogicNat.zero
  46  orbitStep := LogicNat.succ
  47  interpret := narrativeInterpret
  48  interpret_zero := by rfl
  49  interpret_step := by
  50    intro n
  51    show LogicNat.toNat (LogicNat.succ n) = Nat.succ (LogicNat.toNat n)
  52    rfl
  53  orbit_no_confusion := by intro n h; exact LogicNat.zero_ne_succ n h
  54  orbit_step_injective := LogicNat.succ_injective
  55  orbit_induction := by
  56    intro P h0 hs n
  57    exact LogicNat.induction (motive := P) h0 hs n

papers checked against this theorem

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