[AaronBrown]

I'm not sure I understand. Let's take an oversimplified example. Say a player raises in first position if and only if he has:

(1) Any Ace-King or Ace-Queen
(2) Any suited Ace-x
(3) Any pair from 7's to Jacks

Of course, no one is this predictable. But if he was, there are 102 out of 1,326 starting hands that he would raise on if first position. You could compute the probability of any specific hand, say pocket Jacks, by taking the number of ways to form the hand (6) divided by 102. Of course, these computations will change based on the hands you hold.

In theory, you could compute your equity for any of the possible hands for the other player, then weight them by the probability of that hand. In practice, you use rough guesses of the probabilities of the most likely hands to form an idea of what your best action is.

It's silly to worry about which of his hands is best or worst for you, neither you nor he control what he has.