In the first section of J. P. May’s *General algebraic approach to Steenrod operations*, May defines for $\pi\subseteq\Sigma\_r$ an integer $q\in\mathbb{Z}$ and a commutative ring $\Lambda$, the $\Lambda\pi$-module $\Lambda(q)=\Lambda$ with sign action $\sigma\lambda = (-1)^{qs(\sigma)}\cdot \lambda$ where $(-1)^{s(\sigma)}$ is the sign of $\sigma$. 


For a $\Lambda$-chain complex $K$ we consider $K^{\otimes r}(q)= K^{\otimes r}\otimes \Lambda(q)$ with the diagonal action. I assume that this translates to the explicit sign rule for the transposition $\sigma\_{i,i+1}$ in $K^{\otimes r}(q)$
$$\sigma\_{i,i+1}\cdot (a\_1\otimes\dotsb\otimes a\_r) = (-1)^{q+|a\_i|\cdot |a\_{i+1}|}\cdot (a\_1\otimes\dotsb \otimes a\_{i+1}\otimes a\_i\otimes\dotsb\otimes a\_r).$$
Am I correct with this? He later considers cycles $a,b\in K\_q$ and $c\in K\_{q+1}$ with $dc=a-b$. Now let $I$ be the cellular chain complex of the intervall, i.e. $I\_1=\Lambda\langle e\rangle$ and $I\_0=\Lambda \langle e\_0,e\_1\rangle$, and $de=e\_1-e\_0$. We consider the chain map of degree $q$
$$f:I\to K, e\mapsto (-1)^qc, e\_1\mapsto a, e\_2\mapsto b.$$
This satisfies $dfe=(-1)^qfde$ and hence is a chain map. May now claims that $f^{\otimes r}:I^{\otimes r}\to K^{\otimes r}(q)$ is $R\pi$-equivariant. I don’t see why: We have
$$f^{\otimes r}(\sigma\_{i,i+1}\cdot (a\_1\otimes\dotsb\otimes a\_r)) = (-1)^{|a\_i|\cdot |a\_{i+1}|} f(a\_1)\otimes\dotsb\otimes f(a\_{i+1})\otimes f(a\_i)\otimes\dotsb\otimes f(a\_r),$$
whereas on the other side, we have
$$\sigma\_{i,i+1}\cdot f^{\otimes r}(a\_1\otimes\dotsb\otimes a\_r)=(-1)^{q+(|a\_i|+q)\cdot(|a\_{i+1}|+q)}\cdot f(a\_1)\otimes\dotsb\otimes f(a\_{i+1})\otimes f(a\_i)\otimes\dotsb\otimes f(a\_r).$$
There are equal iff $q\cdot (|a\_i|+|a\_{i+1}|)$ is even, but this is not necessarily the case. Concretely, if $q=1$ and $\sigma=\sigma\_{1,2}$, then
$$f^{\otimes 2}(\sigma\cdot e\otimes e\_1) = f^{\otimes 2}(e\_1\otimes e)=a\otimes (-c)\ne a\otimes c=\sigma\cdot (-c)\otimes a=\sigma\cdot f^{\otimes 2}(e\otimes e\_1).$$
What am I missing?



Sign in May’s General algebraic approach to Steenrod operations
@FKranhold You mean I got it right? You had me fooled. I should apologize for leaving that detail to the reader, but let me give two excuses. First, one does not actually need that detail to prove Lemma 1.1(iv). It just answers an obvious question the reader might have about the proof. Second, that paper was from the good old days when things went fast. There was a conference, March 30 to April 4, 1970, for Steenrod's 60th birthday. Its Proceedings were submitted June 15, 1970. No time to polish the writing. I remember Steenrod telling me that mine was the only paper in the Proceedings that he understood. He died the next year.


