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− | + | ==[[Zorn's Lemma]]== | |
− | + | '''Zorn's Lemma''' is a [[set theory | set theoretic]] result which is equivalent to the [[Axiom of Choice]]. | |
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− | + | Let <math>A</math> be a [[partially ordered set]]. | |
− | + | We say that <math>A</math> is ''inductively ordered'' if every [[totally ordered set | totally ordered]] [[subset]] <math>T</math> of <math>A</math> has an upper bound, i.e., an element <math>a \in A</math> such that for all <math>x\in T</math>, <math>x \le a</math>. We say that <math>A</math> is ''strictly inductively ordered'' if every totally ordered subset <math>T</math> of <math>A</math> has a [[least upper bound]], i.e., an upper bound <math>a</math> so that if <math>b</math> is an upper bound of <math>T</math>, then <math>a \le b</math>. | |
− | + | An element <math>m \in A</math> is [[maximal element | maximal]] if the relation <math>a \ge m</math> implies <math>a=m</math>. (Note that a set may have several maximal... [[Zorn's Lemma|[more]]] | |
</blockquote> | </blockquote> |
Revision as of 22:00, 19 December 2007
Zorn's Lemma
Zorn's Lemma is a set theoretic result which is equivalent to the Axiom of Choice.
Let be a partially ordered set.
We say that is inductively ordered if every totally ordered subset of has an upper bound, i.e., an element such that for all , . We say that is strictly inductively ordered if every totally ordered subset of has a least upper bound, i.e., an upper bound so that if is an upper bound of , then .
An element is maximal if the relation implies . (Note that a set may have several maximal... [more]