Higher spinor classes - 528

This work defines the higher spinor classes of an orthogonal representation of a Galois group.

These classes are higher-degree analogues of the Frohlich spinor class, which quantify the difference between the Stiefel-Whitney classes of an orthogonal representation and the Hasse-Witt classes of the associated form.

Jardine establishes various basic properties, including vanishing in odd degrees and an induction formula for quadratic field extensions.

The methods used include the homotopy theory of simplicial presheaves and the action of the Steenrod algebra on mod 2 etale cohomology.