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Published online by Cambridge University Press: 20 November 2018
Building on the work of Nogin, we prove that the braid group ${{B}_{4}}$ acts transitively on full exceptional collections of vector bundles on Fano threefolds with ${{b}_{2}}\,=\,1$ and ${{b}_{3}}\,=\,0$. Equivalently, this group acts transitively on the set of simple helices (considered up to a shift in the derived category) on such a Fano threefold. We also prove that on threefolds with ${{b}_{2}}\,=\,1$ and very ample anticanonical class, every exceptional coherent sheaf is locally free.