 (-10.0) $ ask "P(Cancer(Jerry) | Smoking(George), Friend(Jerry, George))"
mean = (p0 + 
p2 = fromMaybe (-10.0) $ ask "P(Cancer(Jerry) | Smoking(George), Friend(Jerry, George))"
p2 = fromMaybe (-10.0) $ ask "P(Cancer(Jerry) | Smoking(George), Friend(Jerry, George))"