Omega will either award you $1000 or ask you to pay him $100. He will award you $1000 if he predicts you would pay him if he asked. He will ask you to pay him $100 if he predicts you wouldn't pay him if he asked.
Omega asks you to pay him $100. Do you pay?
This problem is roughly isomorphic to the branch of Transparent Newcomb (version 1, version 2) where box B is empty, but it's simpler.
Here's a diagram:
By the way, this bears an interesting similarity to the question of how would you explain the event of your left arm being replaced by a blue tentacle. The answer that you wouldn't is perfectly reasonable, since you don't need to be able to adequately respond to that observation, you can self-improve in a way that has a side effect of making you crazy once you observe your left arm being transformed into a blue tentacle, and that wouldn't matter, since this event is of sufficiently low measure and has sufficiently insignificant contribution to overall expected utility to not be worth worrying about.
So in our case, the question should be, is it desirable to not go crazy when presented with this observation and respond in some other way instead, perhaps to win the Omega Award? If so, how should you think about the situation?