I'm studying stable homotopy category, but I find the language of model category hard to understand. For example, I was suggested reading this (which I call "MMSS")
Michael Mandell, Peter May, Stefan Schwede, Brooke Shipley, Model categories of diagram spectra, Proceedings of the London Mathematical Society, 82 (2001), 441-512 (pdf).
So I return to the classics and read part III of this book
J. F. Adams, Stable homotopy and generalised homology.
In this, Adams constructed the category of CW-spectra. It is fine until he proved Lemma 3.1, the Homotopy Extension Theorem for CW-spectra.
Let $X,A$ be a pair of CW-spectra, and $Y,B$ be a pair of spectra such that $\pi_{*}(Y,B)=0$. Suppose given a map $f:X\to Y$ and a homotopy $h:\operatorname{Cyl}(A)\to Y$ from $f|_A$ to a map $g: A\to B$. Then the homotopy can be extended over $\operatorname{Cyl}(X)$ so as to deform $f$ to a map $X\to B$.
Here $\operatorname{Cyl}(X)=I^{+}\wedge X$. He claimed that $f$ is represented by a function $f': X'\to Y$ (this is just definition), and $h$ by a function $h':\operatorname{Cyl}(A')\to Y$, where $X'\supset A'$, $X'$ is cofinal in $X$ and $A'$ is cofinal in $A$. Here the existence of $h'$ is questionable, since it is not known whether every cofinal subspectra in $\operatorname{Cyl}(A)$ contains $\operatorname{Cyl}(A')$ for some cofinal subspectra $A'$ of $A$ (I couldn't see it myself). Moreover, the proof relies on an argument using Zorn's Lemma, in which the existence of such $h'$ is indispensable.
A quick search tell me that CW-spectra is now called CW-prespectra, and is a special version of sequential spectra. Also, on nLab (see this) they advised to ignore section $III.3$ in Adams' book and follow the treatment in MMSS, so maybe this part of the book is already outdated. My questions are
- Is the original proof correct? For example, one could show the existence of $h'$ somehow.
- If the original proof is wrong, is the theorem still true? Is there a version of it in the modern theory? How can I prove it?
Any help will be appreciated. Also, some advice or sources about this topic would be very kind.
In the comments, I asserted the following.
Proof. For each cell in $K$, let $C_e$ be the intersection of $C$ and $A \wedge e_+$ in $A \wedge K_+$. We may regard $C_e$ as a subspectrum of $A \simeq A \wedge e_+$, and it is cofinal in $A$ since $C$ is cofinal in $A \wedge K_+$. Let $A'$ be intersection of all the $C_e$ as $e$ varies over the cells of $K$. Since $K$ only has finitely many cells, $A'$ is cofinal in $A$, and $A' \wedge K_+$ is a subspectrum of $C$.