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:
Thanks, this looks like a fair summary (though a couple levels too abstract for my liking, as usual).
A note on epistemic relevance. Long ago, when we were just starting to discuss Newcomblike problems, the preamble usually went something like this: "Omega appears and somehow convinces you that it's trustworthy". So I'm supposed to listen to Omega's words and somehow split them into an "epistemically relevant" part and an "observation" part, which should never mix? This sounds very shady. I hope we can disentangle this someday.