Chain Lemma, Quadratic Forms and Symbol Length

We want to bound the symbol length of classes in ${}_{2^{m-1}}Br(F)$ which are represented by tensor products of 5 or 6 cyclic algebras of degree $2^m$. The main ingredients are the chain lemma for quadratic forms, a form of a generalized Clifford invariant and Pfister’s and Rost’s descriptions of 12- and 14-dimensional forms in $I^{3}F$.