A Appendix A Probability
A.1 Random variables
Probability is an essential idea in both information theory and quantum mechanics. It is a highly developed mathematical and philosophical subject of its own, worthy of serious study. In this brief appendix, however, we can only sketch a few elementary concepts, tools, and theorems that we use elsewhere in the text.
In discussing the properties of a collection of sets, it is often useful to suppose that they are all subsets of an overall “universe” set U. The universe serves as a frame within which unions, intersections, complements, and other set operations can be described. In much the same way, ...