Pfister form

Summary

A Pfister form is a quadratic form that is a tensor product of binary forms $\langle 1, -a \rangle$. An $n$-fold Pfister form has dimension $2^n$. Pfister forms are multiplicative: the nonzero values they take form a group. They generate the powers of the fundamental ideal of the Witt ring, and they are the forms that correspond to symbols in Milnor K-theory.