prop_setIdx :: Instance.Instance -> Types.Idx -> Property
prop_setIdx inst idx =
  Instance.idx (Instance.setIdx inst idx) ==? idx
prop_setIdx :: Instance.Instance -> Types.Idx -> Property
prop_setIdx inst idx =
  Instance.idx (Instance.setIdx inst idx) ==? idx
prop_setIdx inst idx =
  Instance.idx (Instance.setIdx inst idx) ==? idx