theorem
proved
tactic proof
eventCost_symm
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formal statement (Lean)
27theorem eventCost_symm (a b : EventState) : eventCost a b = eventCost b a := by
proof body
Tactic-mode proof.
28 by_cases h : a = b
29 · subst h
30 simp [eventCost]
31 · have h' : b ≠ a := by intro hb; exact h hb.symm
32 simp [eventCost, h, h']
33