A standard 52 card deck is shuffled and you and your opponent are dealt two 'hole' cards each. now the next three cards from the deck are exposed (the flop) and it contains two of the deck's four aces.
Does the fact that two aces were exposed make it less likely, more likely, or not important to the question 'what is the probability that my opponent was dealt an ace?'
My gut leads me to think it shouldn't matter - that the cards that were dealt on the flop don't affect what your opponent was dealt in the hole, but I suspect that's not correct and that the presence of the two aces decreases the probability that my opponent has an ace in the hole. Not sure by how much.