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Sep 19, 2020 at 2:45 vote accept Victor TC
Sep 19, 2020 at 17:08
Sep 19, 2020 at 1:57 comment added Tom Goodwillie A very slightly different point of view: A spectrum $C$ is $p$-complete iff $F(A,C)=0$ for every $S/p$-acyclic spectrum $A$, i.e. every $A$ such that $A/p=0$. A spectrum $T$ is $p$-torsion if and only if $F(T,A)=0$ for every $S/p$-acyclic $A$. So if $T$ is $p$-torsion then for every $U$ the spectrum $F(T,U)$ is $p$-complete since, for every such $A$, $F(A,F(T,U))=F(T,F(A,U))=0$. The key point is that $F(A,U)$ is always $S/p$-acyclic if $A$ is $S/p$-acyclic. ($F(A,U)/p$ is a shift of $F(A/p,U)$.)
Sep 18, 2020 at 23:25 history edited Piotr Pstrągowski CC BY-SA 4.0
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Sep 18, 2020 at 23:23 comment added Tim Campion (Sorry I deleted my comment -- I was trying to edit it to say thanks for the addition, but went longer than 5 minutes and then ended up deleting it!) Interesting that both arguments for $T$ $p$-torsion $\Rightarrow F(T,U)$ $p$-complete seem to rely on the fact that $M(p)$ is a shift of its own Spanier-Whitehead dual -- especially in your formulation, this seems like the least "formal" fact used.
Sep 18, 2020 at 23:16 comment added Piotr Pstrągowski I added an argument using Maschke's theorem.
Sep 18, 2020 at 23:14 history edited Piotr Pstrągowski CC BY-SA 4.0
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Sep 18, 2020 at 23:00 history answered Piotr Pstrągowski CC BY-SA 4.0