algebraic cone; monoid action; group action; orbit; action with unique fixed point; algebra automorphism; stable ideal; irreducible algebraic variety quadratic form; Witt ring; fundamental ideal; Pfister form; Witt index; higher Witt indices; generic splitting; height of a quadratic form; stable birational equivalence; Chow motif; Tate motif; Rost motif; homogeneous variety; Rost's nilpotence theorem; Steenrod operation; motivic equivalence 