This document discusses key concepts related to sets including: - Cardinality refers to the number of elements in a set and is denoted by n(A). - Two sets are equivalent if they have the same number of elements. - A set A is a subset of set B if every element of A is also an element of B, denoted by A ⊆ B. - A set A is a proper subset of set B if A is a subset of B but the sets are not equal, denoted by A ⊂ B. - The universal set U refers to all elements being considered in a problem. - The complement of a set A, denoted by A', refers to