Statisticians often use the set theory to represent relationships among events (collections of outcomes of an experiment). This is usually written in the following notation, in which *A* and *B* are two events in the sample space *S:*

*A*∪*B*, or “either *A* or *B* occurs, or both”; this is said as “A union B” in set theory;
*A*∩*B*, or “both *A* and *B* occur”; this is said as “A intersection B” in set theory;
*A*⊆*B*, or “if *A* occurs, so does *B* occur”; this is said as “A is a subset of B” in set theory;
*A*’, or “*A* does not occur.”