# Mapping into Hurewicz cofibrations.

In Strøm's paper "The Homotopy Category is a Homotopy Category" he proves (Lemma 4) that if $Y$ is compact and if $i:A\to X$ is a cofibration, then the induced map $$i_*: A^Y \to X^Y$$ is also a cofibration.

The proof goes like this: he's already shown that $i:A\to X$ is a cofibration if and only if there is a function $u: X\to I$ such that $A = u^{-1}(0)$ and a deformation $H:X\times I \to X$ of $X$ that is constant on $A$ and pushes $U = u^{-1}([0,1))$ into $A$. Then he defines $$v(\alpha) = \sup \{ i\circ \alpha(Y) \} \qquad \mathrm{and}\qquad K (\alpha, t) (y) = H(\alpha(y), t).$$ This shows that $i_*$ is a cofibration since $v^{-1}(0) = A^Y$ and $K$ deforms $V = v^{-1}([0,1))$ into $A^Y$. When I try to prove that $v$ is continuous, it's very helpful to have the compactness of $Y$.

My question is: can the compactness hypothesis be dropped, perhaps if we work with compactly generated spaces?

EDIT: Ok, I see the problem with noncompact domains.
The space $I^{\mathbb{R}}$ is a good example. Functions in the set $\mathcal{U}(C,V)$ ($C\subseteq \mathbb{R}$ compact, $V\subseteq I$ open) are only limited on $C$, and so can take very large values elsewhere. You can cut this down a bit by taking intersections, and this does the job for compact domains, but you can only take finitely many. These spaces being as nice as can be, this is a dead question.

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I hope you don't mind that I got rid of the empty set in the name of Arne Strøm. – José Figueroa-O'Farrill Dec 13 '10 at 19:20
I know that $\varnothing$ was originally ø, but they are rendered in different fonts and so are not interchangeable. I apologise if it was meant as a witticism, but it looked horrendous. – Loop Space Dec 13 '10 at 19:20
(José - simultaneous edits there, I think.) – Loop Space Dec 13 '10 at 19:25
@all: No, I just didn't know how to make an ø (still don't, that's cut-and-paste). – Jeff Strom Dec 13 '10 at 19:50
Jeff: you can use HTML entities in questions and answers, so &oslash; will work. (It doesn't work in comments for some bizarre reason though - I had to go to José's user page to find an e-acute to use!) – Loop Space Dec 13 '10 at 20:23