theorem
proved
tactic proof
actionCost_symm
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formal statement (Lean)
28theorem actionCost_symm (a b : ActionState) : actionCost a b = actionCost b a := by
proof body
Tactic-mode proof.
29 by_cases h : a = b
30 · subst h
31 simp [actionCost]
32 · have h' : b ≠ a := by intro hb; exact h hb.symm
33 simp [actionCost, h, h']
34