2.1 Set Theory

• A set is a collection of elements ($\{\xi_1, \xi_2, ..., \xi_n\}$)

• Elements can be anything… apples, real numbers, functions, sets!

• B is a subset of A, denoted $B \subseteq A$ if every member of B is also a member of A.

A <- c(1,2,3,4,5,6)
B <- c(2,4,6)
all(B %in% A)

## [1] TRUE

all(A %in% B)

## [1] FALSE