Applying Zorn's Lemma (Maximal Subspace)

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In summary, the Zorn's lemma is a tool that can be used to find an upper bound for a given chain in a partially ordered set.
  • #1
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Homework Statement


Suppose that V is a vector space, W and X are subspaces with X contained in W. Show that there is a subspace U of V which is maximal subject to the property that U intersect W equals X.

Homework Equations


N/A

The Attempt at a Solution


I know this uses Zorn's Lemma but I can't see how to apply it.

Thanks for any help in advance!
 
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  • #2
So what do we need to apply Zorn's lemma? A partially ordered set in which every chain has an upper bound. Let's let our partially ordered set be the family of all subspaces of V whose intersections with W gives X ordered by inclusion. Given a chain in this poset, can you find a natural upper bound?
 
  • #3
rochfor1 said:
So what do we need to apply Zorn's lemma? A partially ordered set in which every chain has an upper bound. Let's let our partially ordered set be the family of all subspaces of V whose intersections with W gives X ordered by inclusion. Given a chain in this poset, can you find a natural upper bound?

Would a natural upper bound for this poset be the subspace U such that U contains X and V-{W-X}?
 
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  • #4
We're trying to prove that U exists, so we can't use it as the upper bound here. Also, you don't have to find an upper bound for the whole poset, that's what Zorn's lemma gives. You just need to find an upper bound for an arbitrary chain in the poset. A subset S of our poset is a chain if [tex]A,B \in S[/tex] implies that either [tex]A\subseteq B[/tex] or [tex]B \subseteq A[/tex]. What can you say about the union of a family of increasing subpsaces?
 
  • #5
Wouldn't the union of increasing subspaces tend to some infinite subspace?
 
  • #6
Take out infinite (which is not necessarily true) and you've got it.
 
  • #7
Thanks for your help :)
 

FAQ: Applying Zorn's Lemma (Maximal Subspace)

What is Zorn's Lemma?

Zorn's Lemma is a mathematical principle that states that every partially ordered set that satisfies a particular condition has a maximal element. It is often used in mathematical proofs to show the existence of a maximal element in a set.

How is Zorn's Lemma applied to finding maximal subspaces?

To apply Zorn's Lemma to finding maximal subspaces, we first define a partial ordering on the set of subspaces. Then, we show that every chain (a set of subspaces that are nested within each other) has an upper bound. Finally, we use Zorn's Lemma to conclude that there exists a maximal element in the set of subspaces.

What is a maximal subspace?

A maximal subspace is a subspace within a vector space that is not properly contained in any other subspace. In other words, it is the largest possible subspace that can be formed within a given vector space.

What is the significance of finding maximal subspaces?

Finding maximal subspaces is significant because it allows us to identify the largest possible subspaces within a vector space. This can be useful in understanding the structure of the vector space and in solving problems related to linear algebra.

Are there any limitations to applying Zorn's Lemma to finding maximal subspaces?

One limitation of applying Zorn's Lemma to finding maximal subspaces is that it can only be applied to a finite-dimensional vector space. It cannot be used for infinite-dimensional vector spaces. Additionally, Zorn's Lemma does not provide a constructive method for finding maximal subspaces, so it may not be helpful in practical applications.

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