# Geometry and Arithmetic

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#### DOI: 10.4171/119-1/3

Non-rationality of the symmetric sextic Fano threefold

Arnaud Beauville[1]

(1) Université de Nice, France

We prove that the symmetric sextic Fano threefold, defined by the equations $\sum X_i=\sum X_i^2=\sum X_i^3=0$ in $\mathbb{P}^6$, is not rational. In view of the work of Prokhorov [P], our result implies that the alternating group $\mathfrak{A}_7$ admits only one embedding into the Cremona group $\mathrm{Cr}_3$ up to conjugacy.

Keywords: Rationality questions, unirational varieties, Cremona group