Conditional entropy of a countable measurable partition
= Conditional entropy of a countable measurable partition
{title2=$H_\mu(\xi\mid\mathcal G)$}
The conditional entropy is the integral of the <conditional information function>. Its chain rule expresses the entropy of a <join of measurable partitions> as unconditional entropy plus conditional entropy. <Conditioning reduces entropy>, also for countable partitions of finite entropy.