# Compact subset of a locally compact space

1. Nov 6, 2007

### ehrenfest

1. The problem statement, all variables and given/known data
How would I prove that if X is locally compact and a subset of X, V, is compact, then there is an open set G with $$V \subset G$$ and closure(G) compact?

EDIT: X is also Hausdorff (which with local compactness implies that it is regular) if that matters

2. Relevant equations

3. The attempt at a solution

Last edited: Nov 6, 2007
2. Nov 6, 2007

### morphism

If X is regular, then given a point x in X and a nbhd* U of x, we can find a nbhd W of x whose closure sits in U. Do this for each x in V. Now use the facts that X is locally compact and that V is compact.

(*: I'm using nbhd to mean an open set containing x.)

Last edited: Nov 6, 2007
3. Nov 6, 2007

### ehrenfest

So because X is locally compact, we have a nbhd around every point x whose closure is compact, call it N_x. Now, like you said, for all x in V, we take find a nbhd around x, call it M_x whose closure sits in N_x.

The union of M_x over x in V form an open cover of V, so we have a finite subcover, say {M_x_1 to M_x_n}. Union M_x_i is an open set that contains V. Is its closure compact, though?

4. Nov 6, 2007

### ehrenfest

Okay. I see why the closure is compact. But also, how would I prove that the boundary of our open set G is compact?

5. Nov 6, 2007

### morphism

It's a closed subset of a compact space, isn't it?

6. Nov 7, 2007

### ehrenfest

Got it. Thanks.