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theorem proved tactic proof

narrativeCost_symm

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formal statement (Lean)

  27theorem narrativeCost_symm (a b : NarrativeBeat) : narrativeCost a b = narrativeCost b a := by

proof body

Tactic-mode proof.

  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

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depends on (2)

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