什么是佐恩(Zorn)引理?
(2018-09-04 12:26:55)什么是佐恩(Zorn)引理?
愿我们共勉之。
袁萌
附:佐恩引理
We will use a form of the Axiom of Choice(选择公理) called Zorn’s Lemma(佐恩引理). A nonempty set X of sets(集合的集合) is called a chain(链) if for any two sets x, y ∈ X, either x ⊆ y or y ⊆ x.
Zorn’s Lemma. Let Y be a nonempty set of sets such that for any chain X ⊆ Y , the union of X belongs to Y . Then Y has a maximal element y, that is, a set y ∈ Y such that no member of Y properly contains y.
(这是佐恩引理的准确陈述)