  Compression of integer sets and sequences has been extensively studied for
settings where elements follow a uniform probability distribution. In addition,
methods exist that exploit clustering of elements in order to achieve higher
compression performance. In this work, we address the case where enumeration of
elements may be arbitrary or random, but where statistics is kept in order to
estimate probabilities of elements. We present a recursive subset-size encoding
method that is able to benefit from statistics, explore the effects of
permuting the enumeration order based on element probabilities, and discuss
general properties and possibilities for this class of compression problem.
