ch 2
A collection of events is independent if and only if learning that some of them occur
does not change the probabilities that any combination of the rest of them occurs.
Equivalently, a collection of events is independent if and only if the probability of the
intersection of every subcollection is the product of the individual probabilities. The
concept of independence has a version conditional on another event. A collection
of events is independent conditional on B if and only if the conditional probability
of the intersection of every subcollection given B is the product of the individual
conditional probabilities given B. Equivalently, a collection of events is conditionally
independent given B if and only if learning that some of them (and B) occur does
not change the conditional probabilities given B that any combination of the rest of
them occur. The full power of conditional independence will become more apparent
after we introduce Bayes’ theorem in the next section.
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