On the Brauer-Manin obstruction for degree four del Pezzo surfaces

Jörg Jahnel, Damaris Schindler

We show that, for every integer $1\le d\le 4$ and every finite set $S$ of places, there exists a degree $d$ del Pezzo surface $X$ over $\mathbb{Q}$ such that ${\rm Br}(X)/{\rm…