= Adem relations
{c}
{title2=$\operatorname{Sq}^a\operatorname{Sq}^b=\sum_t\binom{b-t-1}{a-2t}\operatorname{Sq}^{a+b-t}\operatorname{Sq}^t\quad(a<2b)$}
These mod-two identities rewrite nonadmissible products of <Steenrod squares>. For example, $\operatorname{Sq}^1\operatorname{Sq}^1=0$, $\operatorname{Sq}^1\operatorname{Sq}^2=\operatorname{Sq}^3$, and $\operatorname{Sq}^1\operatorname{Sq}^3=0$. In general the sum ranges over $0\leq t\leq\lfloor a/2\rfloor$ and coefficients are reduced modulo two.
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