UDT doesn't handle non-base-level maximization vantage points (previously "epistemic vantage points") for blackmail - you can blackmail a UDT agent because it assumes your strategy is fixed, and doesn't realize you're only blackmailing it because you're simulating it being blackmailable.

I'm not so sure about this one... It seems that UDT would be deciding "If blackmailed, pay or don't pay" without knowing whether it actually will be blackmailed yet. Assuming it knows the payoffs the other agent receives, it would reason "If a pay if blackmailed...I get blackmailed, whereas if I don't pay if blackmailed...I don't get blackmailed. I therefore should never pay if blackmailed", unless there's something I'm missing.