In the section 'Predicates as events' the function is_prime is defined, but the examples use prime which was previously defined as a set the primes up to 13. This means the probabilities shown for the 20 sided die are incorrect. For example:

P(prime, die(20))

0.3

The correct probability is 0.4:

>>> len({2,3,5,7,11,13,17,19})/20
0.4

Thanks for posting all these notebooks!