二元关系的论域(universe) The set of all possible objects that are considered in the context in which we work is called the universe. 问题2：就二元关系R二A×B而言，其论域是什么？ 通常情况下，我们讨论A=B的一类特殊关系较多 "S is a relation on a set x"is one way of saying that S is a subset of X×X二元关系的论域（universe） 问题2：就二元关系𝑹 ⊆ 𝑨 × 𝑩而言，其论域是什么？ 通常情况下，我们讨论A=B的一类特殊关系较多 “S is a relation on a set 𝑿” is one way of saying that S is a subset of 𝑿 × 𝑿 The set of all possible objects that are considered in the context in which we work is called the universe