property ShouldUseEntries
  nondet (start iteratingKeys)
  start -> start: *
  start -> gotKeys: "Map.keySet"(M, S) => m := M; s := S
  gotKeys -> iteratingKeys: "Set.iterator"(S, I) when S == s => i := I
  iteratingKeys -> iteratingKeys: *
  iteratingKeys -> gotOneKey: "Iterator.next"(I, K) when I == i => k := K
  gotOneKey -> error: ".*Map.get"(M, K, IgnoreRet) when M == m && K == k