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