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I have a problem with understanding Cohen's definition, as written in "The Homology of Iterated Loop Spaces" by Cohen, Lada and May (Part III, chapter 5, at the end of chapter).

So in order to define loop operations on a $n$-fold loop-suspension space $X$ in the vein of "A General Algebraic Approach to Steenrod Operations" I proceed as follows.

  1. I have a little $n$-disks operad acting on $X$, so I have a map $D_n(r)\times_{\Sigma_r}X^r\to X$.

  2. Out of this, I should derive a map of $\mathbb{Z}_p\pi$-complexes, where $\pi$ is cyclic of order $r$: $$ \theta :W^{(n)}\otimes C_*(X)^{\otimes r}\to C_*(X), $$ which is subject to the conditions described in "A General Algebraic Approach..." and allows me to define loop operations. Here $W^{(n)}$ is a $n$-th skeleton of a $\mathbb{Z}_p\pi$-free resolution of $\mathbb{Z}_p$.

  3. In refered work, Cohen compute the cohomology of braid spaces. Then he takes the dual elements to the generators of image in $H^*(B\Sigma_r;\mathbb{Z}_p(q))$ and this allows him to define the loop operations.

So what I do not understand here is connection between points 3 and 2. Having all of Cohen's work done, how does it fit to "A General Algebraic Approach..." framework?

Sorry for any mistakes, I'm still a child in this area.

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  • $\begingroup$ ``The general approach to Steenrod operations'' refers to May's 1967 paper in which the machinery of operads was introduced but without any given name! (2) I suppose the operad action gives you maps $C_n(r)\times_{\Sigma_r}X^r\to X$ and step 2 in your question is to realise this map on the level of chain complexes. The spaces $C_\infty(r)$ serves as a model for $E\Sigma_r$, so somehow you may use this to see why $B\Sigma_r$ is showing up. $\endgroup$
    – user51223
    Commented Oct 18, 2018 at 4:58
  • $\begingroup$ (3) The brain group is related to the symmetric group by an epimorphism whose kernel is the pure braid group. So, that also can give some map in homology or cohomology and you may ask about the image of generators. $\endgroup$
    – user51223
    Commented Oct 18, 2018 at 4:59

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