Nick, the reason there are no such systems (which are at least as intelligent as us) is that we are not complicated enough to manage to understand the proof.
This is obvious: the AI itself cannot understand a proof that it cannot do action A. For if we told it that it could not do A, it would still say, “I could do A, if I wanted to. And I have not made my decision yet. So I don’t yet know whether I will do A or not. So your proof does not convince me.” And if the AI cannot understand the proof, obviously we cannot understand the proof ourselves, since we are inferior to it.
So in other words, I am not saying that there are no rigid restrictions. I am saying that there are no rigid restrictions that can be formally proved by a proof that can be understood by the human mind.
This is all perfectly consistent with physics and math.