# Homework Help: Closed subset of XxY?

1. May 27, 2007

### pivoxa15

1. The problem statement, all variables and given/known data
Let f:X->Y be a cts map from a topological space X to a Hausdorff space Y. Prove that the graph L={(x,y) in XxY: y=f(x)} is a closed subset of XxY.

3. The attempt at a solution
Hausdorff space are linked with open sets so how do you prove closeness in XxY?

2. May 27, 2007

### matt grime

This is not important but since open sets are linked to closed sets, then anything to do with closed sets has some relation with open sets. You understand that a set is open if and only if its complement is closed?

So, start with L. What does it mean to be closed? There are many things to try, so write a few of them down and think about it for a while (perhaps a day or so, if need be - answers don't just magically appear instantly in people's minds).

3. May 27, 2007

### pivoxa15

If only the assignment is not due tomorrow morning.

4. May 27, 2007

### matt grime

L is closed if and only if its complement is open. Suppose that the complement is not open. What does that mean?

5. Apr 25, 2010

### complexnumber

Can you give more hint?

Why can't we use the proof in Banach space in the following link?
http://myyn.org/m/article/proof-of-closed-graph-theorem/ [Broken]

Last edited by a moderator: May 4, 2017