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:
When a program takes explicit input, you can look at what the program does if you pass this or that input, even if some inputs will in fact never be passed.