@Steph_iscrypto "set theory, by the principle of extensionality, two sets are equal if they have the same elements (that is, neither of them has an element not in the other). As a result, there can be only one set with no elements, hence the usage of "the empty set" rather than "an empty set".
@Steph_iscrypto In mathematics, the empty set or void set is the unique set having no elements; its size or cardinality (count of elements in a set) is zero.