  We generate fixed three- and four-light-flavour sets of partons using
MRST2004 partons as input. We show that it is important to set n_f=3 in the
strong coupling, as well as in the splitting and coefficient functions, in
order to obtain a consistent set of fixed-flavour partons. We compare the
description of data using partons in both variable- and
fixed-flavour-number-schemes.
