\BOOKMARK [1][-]{section*.1}{Introduction}{}% 1 \BOOKMARK [1][-]{section.1}{1. Preliminaries}{}% 2 \BOOKMARK [1][-]{section.2}{2. The twisted gamma-filtration}{}% 3 \BOOKMARK [1][-]{section.3}{3. Algebras with orthogonal involution}{}% 4 \BOOKMARK [1][-]{section.4}{4. Construction of a torsion element}{}% 5 \BOOKMARK [1][-]{section*.2}{References}{}% 6