👉 In mathematics, a subset S of a set X is said to be a subset of X (or equivalently, to be contained in X) if every element in X is also an element of S. A set that contains all its own elements is called a universal set. For example, the set {a, b} of all ordered pairs of distinct elements from the set {1, 2, 3}, such that the first element is less than the second, is a subset of
