Solution
= Solution
A <pi-system> is a family closed under finite intersections. A <Dynkin system> contains the whole underlying set, is closed under complements in it, and is closed under countable pairwise-disjoint unions.
= Solution
A <pi-system> is a family closed under finite intersections. A <Dynkin system> contains the whole underlying set, is closed under complements in it, and is closed under countable pairwise-disjoint unions.