set notation

universal set of everything

∅

empty set (a set with no elements)

eg - {x is an even prime bigger than 5} = ∅

upper case letters

represent sets

lower case letters

represent elements

n(A)

number of elements in set A

a ∈ A

a is an element of A (a is in the set A)

A ⊆ B

A is a subset of B

every element in A is also in B

A ⊂ B

A is a proper subset of B

A is a subset of B but not the same as B

cross through a symbol

not true

A ∩ B

intersection (overlap) of A and B

A ∪ B

union of A and B (everything in A or B or both)

A'

not A (everything outside A)