A categorical Künneth formula for constructible étale sheaves
Timo Richarz, Jakob Scholbach
Drinfeld's lemma measures the failure of the K\"unneth formula for the
\'etale fundamental group of schemes in characteristic $p>0$ in terms of
equivariance data under partial Frobenius morphisms. In this note, we promote
Drinfeld's lemma to a K\"unneth type equivalence of derived categories of
constructible Weil sheaves with $\bar F_\ell$-coefficients or $\bar
Q_\ell$-coefficients for $\ell\not = p$.