The generic quadratic form of even dimension n with trivial discriminant over
an arbitrary field of characteristic different from 2 containing a square root
of -1 can be written in the Witt ring as a sum of 2-fold Pfister forms using
n-2 terms and not less. The number of 2-fold Pfister forms needed to express a
quadratic form of dimension 6 with trivial discriminant is determined in
various cases.Comment: 13 page
