So the probability of, I'll call it heads, heads, so I get two heads in a row, given that I have a fair coin. It looks like very fancy notation, but it's just like, look, if you knew for a fact that that coin you had is absolutely fair, that it has a 50% chance of coming up heads, what is the probability of getting two heads in a row? Well, then we can just say, well, that's just going to be 50%. So 50% times 50%, which is equal to 25%. Now, what is the probability that you, so if you want to know what is the probability that you picked a fair coin and you got two heads in a row? So given that you have a fair coin, it's a 25% chance that you have two heads in a row. But the probability of picking a fair coin and then given the fair coin getting two heads in a row will be the 5 8ths times the 25%.