In this chapter we review several mathematical topics that form the foundation of probability and mathematical statistics. These include the algebra of sets and functions, general relations with special emphasis on equivalence relations and partial orders, and some basic combinatorial structures such as permuations and combinations.
Combinatorics is a rich and beautiful mathematical subject in its own right, not just because of its connection to probability.
Later generations will regard set theory as a disease from which one has recovered.--Henri Poincaré