?

Here an interesting odds question (probably pretty tough to calculate too).

Anyone know how to calculate the odds that someone else holds top-hand with two pair better than your two pair when both your pairs, and your opponents pairs are disguised?

On the Flop?
On 4th?
On the river?

What are the odds that the final result will be:
(i) tie with the bottom pair and lose on the top pair?
(ii) tie on the top pair, but lose on the bottom pair?