So what is A and B in the problem we're trying to figure out? We want to try to figure out the probability that I picked out a fair coin given that I got 4 out of 6 heads. So in this situation, A is that I got a fair coin. A is equal to picked fair coin. And then B is equal to 4 out of 6 heads. So in order to figure out the probability that I picked a fair coin given that I got 4 out of 6 heads, I have to know the probability of getting 4 out of 6 heads given that I picked the fair coin times the probability of picking out a fair coin divided by the probability of getting 4 out of 6 heads in general. So this is probably the hardest part to figure out, and we will, along the way, we'll actually probably figure out the top two terms.