This. Constraining the demon to two responses can't work. The demon needs to be able to give an answer with at least as much information as the entire universe'

This. Constraining the demon to two responses can't work. The demon needs to be able to give an answer with at least as much information as the entire universe's state -- not yes or no answers. The issue with the person only exists because the person's actions cannot be represented with a single bit of information. But the person cannot hope to outsmart the demon if it's response has more bits of information than the person can possibly respond with.